Category 6â„¢

Shear rules!

By: JeffMasters, 2:18 PM GMT on July 30, 2005

The tropical wave near Puerto Rico that was close to becoming a tropical depression yesterday is looking very disorganized this morning, and I imagine NHC will cancel the reconnaissance mission that was scheduled to fly into it this afternoon. The wave was probably hurt by its interaction with the big islands of Puerto Rico and Hispanolia, but the primary reason for its demise was the large area of high wind shear that pushed down on it from the north. This morning's wind shear analysis from University of Wisconsin's CIMSS shows a large upper level cold-cored low pressure system just north of Puerto Rico, which is bringing wind shear values of up to 50 knots over the northern portion of the tropical wave. Usually, wind shear values above 20 knots are sufficient to keep a tropical depression from forming, so it is no wonder this tropical wave had trouble last night as the big cold low slid to the south and brought such strong shearing winds with it.

The wave is continuing to the west and bringing heavy rains to Hispanolia, but the path in front of it has plenty of strong shearing winds, so development is unlikely. Similarly, the rest of the tropics have some of the highest levels of shear we've seen this hurricane season, so it looks like a quiet next few days. With the demise of Franklin last night, today is the first tropical storm-free day since July 2!

Dr. Jeff Masters

TD #8 slow to come...

By: JeffMasters, 11:27 PM GMT on July 29, 2005

The Air Force Hurricane Hunter mission investigating the tropical wave near Puerto Rico did not find a closed circulation indicating a tropical depression had formed this afternoon, which is not surprising given the sparse cloud cover associated with this system. Still, the cloud pattern does show a good degree of organization and upper-level winds are still favorable, so a tropical depression could form tomorrow morning. The timing of formation will be critical. If the storm just gets its act together as it hits Hispanolia, will it be able to survive crossing the island and reform on the other side? I've never seen a tropical depression try to form basically on top of Hispanolia, which appears as if what this storm wants to try to do. I'm not sure if a developing tropical depression can survive crossing the island, and I bet in most cases it will not. However, this is the Hurricane Season of 2005, so consider it likely.

The long range radar loop out of San Juan, PR, should be interesting to watch tonight. About 10-11pm convection should start to pick up, as we head into the usual midnight - 4am maximum in thunderstorm activity over the tropics. This may be enough to trigger the extra low-level convergence needed to get this storm spinning up into a tropical depression.

I figured out how to plot the early model runs (well, at least the BAMM and GFDL), I will try to keep this image updated.

Jeff Masters

TD 8? Not yet...

By: JeffMasters, 4:05 PM GMT on July 29, 2005

Satellite imagery of the tropical wave approaching Puerto Rico shows a less impressive system than yesterday. The wave covers less area, has reduced upper level outflow, and is battling increased wind shear. However, the dry air on the wave's west side that was inhibiting thunderstorm development last night is less apparent on today's water vapor satellite imagery.

The most most impressive sign of organization of this wave is in the pressure falls observed over the Lesser Antilles islands this morning. A plot of the past week's pressures at one of our personal weather stations in Anguilla, an island in the northern Lesser Antilles about 150 miles east of Puerto Rico, shows a significant pressure fall this morning:

Keep in mind that it is a bit tricky to interpret pressure readings in the tropics. The pressure plot shows a curious regular oscillation with amplitude 1 mb, and a peak twice per day at about 11am and 11pm local time. This oscillation is due to the presence of atmospheric tides in the atmosphere. Like tides in the ocean, atmospheric tides move as a wave around the planet with a very regular period in sync with the Earth's rotation rate. The atmospheric tides we see in the Anguilla data are primarilly due to solar heating of the atmosphere. When the sun rises and starts heating the air, the air expands in response, lowering the pressure in the vicinity, and pushing a wave alternating high and low pressure air all the way around the globe. The amplitude of this wave is highest--about 1.5 mb--where the sun's heating is greatest, near the equator. The wave's minimum amplitude of about 0.5 mb occurs near the poles. The period of the wave is 12 hours.

Mentally remove the wriggles from the pressure plot above, and you can see that the drop in pressure this morning in Anguilla was not due just to the atmospheric tidal effect, but must also have had a component due to a low pressure system moving in. Similar pressure falls are being observed on nearby islands that the tropical wave is affecting, such as St. Maarten.

A hurricane hunter aircraft will investigate the area at 4pm today to see if a tropical depression is forming. If a depression does form, its potential track is highly uncertain. The GFS model maintains that it will track WNW and threaten the East Coast, while the ECMWF has the system moving into the Gulf of Mexico. The GFDL model moves the system into the Bahamas and disipates it in 36 hours. In any case, if a depression does form, it will have some significant barriers to overcome in order to intensify. If the storm moves north, there is a large upper-level trough with strong shearing winds to contend with. If the storm stays further south, interaction with the land masses of Puerto Rico and Hispanolia will hinder it.

Dr. Jeff Masters

Tropical Depression Eight on the way?

By: JeffMasters, 5:03 PM GMT on July 28, 2005

Tropical Storm Franklin continues its defiant trek across the Atlantic, but its days are surely numbered. It's currently moving over warm Gulf Stream waters, but in two days time, it will pass north of the Gulf Stream and encounter waters below 80F, which cannot sustain a tropical storm.

With Franklin likely to finally die, that means it must be time for a new storm to develop--after all, this is the Hurricane Season of 2005. We've had at least one active tropical storm continuously since Cindy formed on July 3, making this year's stretch of 25 straight days with tropical cyclone activity the longest such July stretch on record. The previous record was in 1979, with 21 consecutive days of July activity. And sure enough, we have a potential Tropical Depression Eight brewing in the Atlantic. The tropical wave near 20N 50W approaching the Lesser Antilles began forming a more concentrated area of thunderstorms last night, and that trend has continued today as the wave moves steadily west-northwestward at 15 mph. An impressive upper-level outflow channel has opened to the north, and satellite loops show high cirrus clouds blowing off the tops of the wave's thunderstorms streaming to the northeast. There is no obvious circulation yet. The wave is over 28 - 29C water, with warmer 29 - 30C water ahead of it. By tonight, the wave looks to have lower wind shear affecting it as well, and I expect we will have Tropical Depression Eight by tomorrow night.

If the storm develops, the immediate threat will be to the northern Leeward Islands and Puerto Rico. However, the steering flow looks to be west-northwesterly over the system the next few days, and the GFS model (which does not develop it and keeps it a tropical wave) has the system tracking north of the islands and approaching the East Coast of the U.S. At this point, it's anybody's guess what part of the East Coast might be most at risk. There is a moderately strong trough pushing off of the East Coast on Tuesday, and it's quite possible that this trough would recurve the storm out to sea before it hits the coast. I think the Hurricane Season of 2005 owes us a break!

Dr. Jeff Masters

Today's tropics, and retiring Emily's name

By: JeffMasters, 4:15 PM GMT on July 27, 2005

The tropics remain relatively quiet. Franklin, who keeps saying "I'm not dead yet!", continues to stagger along as a bare minimal tropical storm. The two tropical waves I pointed out yesterday are still looking interesting, particularly the one closer to the Leeward Islands. This wave has a very broad circulation now, although it still lacks much in the way of convection. I'll talk more about these waves if they start to show more organization.

I'd also like to mention that the comments to this blog have gotten too excessive to be of value for the majority of our readers. I encourage those of you who are trying to set a record for a high number of posts to resist that urge. It is difficult for people to find some useful URL or question that needs answering, due to the large number of posts. However, I am pleased with the general tone of all the posts; flame wars have not been a problem. Thanks. On to today's topic--

Will Emily's name get retired?
Hurricanes began getting names in 1950, when the U.S. Weather Bureau began using the phonetic alphabet (Able-Baker-Charlie). In 1953, womens names were substituted, and in 1979, the World Meteorological Organization (WMO) and the U.S. National Weather Service switched to a list of names that also included men's names. The current list of names recycles every six years, unless a hurricane gets its name retired. Any nation impacted by a severe hurricane can lobby the WMO to have the name of that hurricane retired. From 1950 - 2004, 62 hurricanes have had their names retired. The list includes one tropical storm, Allison of 2001, that caused billions in damage from its heavy rains. Only one hurricane has had its name retired in the Eastern Pacific--Hurricane Kenna of 2002, which hit Mexico.

The storm with the most appearances so far is Arlene, which has appeared nine times: 1959, 1963, 1967, 1971, 1981, 1987, 1993, 1999, 2005, and will come again in 2011. It took Emily five tries to have her name retired, and I'm sure the WMO will retire both Emily and Dennis of 2005. These will be the only July hurricanes to ever have their name retired. One June storm, Audrey of 1957, had her name retired.

Below is a list of Atlantic Ocean retired names, the years the hurricanes occurred, and the areas they affected. Keep in mind that a large number of destructive storms occurred before naming began in 1950, and are not included on this list. I'll add a link for this list to the tropical page.

Jeff Masters

Atlantic Storms Retired Into Hurricane History

Emily (2005): Grenada, Mexico
Dennis (2005): Cuba, Florida
Jeanne (2004): Florida
Ivan (2004): Grenada, Cayman Islands, Cuba, Alabama, Florida
Frances (2004): Florida
Charley (2004): Cuba, Florida
Juan (2003): Nova Scotia
Isabel (2003): North Carolina, Virginia, Maryland
Fabian (2003): Bermuda
Lili (2002): Cuba, Louisiana
Isidore (2002): Cuba, Mexico, Louisiana
Michelle (2001): Cuba, Bahamas
Iris (2001): Belize
Allison (2001): Texas
Keith (2000): Belize, Mexico
Lenny (1999): Virgin Islands, St. Maartin/St. Martin, Anguilla
Floyd (1999): North Carolina
Mitch (1998): Central America, Nicaragua, Honduras
Georges (1998): Lesser Antilles, Puerto Rico, Hispanolia, Cuba, Mississippi
Hortense (1996): Puerto Rico, Dominican Republic
Fran (1996): North Carolina
Cesar (1996): Nicaragua
Roxanne (1995): Mexico
Opal (1995): Florida
Marilyn (1995): Virgin Islands, Leeward Islands
Luis (1995): Leeward Islands
Andrew (1992): Bahamas, South Florida, Louisiana
Bob (1991): North Carolina, Northeast U.S.
Klaus (1990): Martinique
Diana (1990): Mexico
Hugo (1989): Antilles, South Carolina
Joan (1988): Curacao, Venezuela, Colombia, Nicaragua (Crossed into the Pacific)
Gilbert (1988): Lesser Antilles, Jamaica, Yucatan Peninsula, Mexico
Gloria (1985): North Carolina, Northeast U.S.
Elena (1985): Mississippi, Alabama, Western Florida
Alicia (1983): North Texas
Allen (1980): Antilles, Mexico, South Texas
Frederic (1979): Alabama and Mississippi
David (1979): Lesser Antilles, Hispañola, Florida and Eastern U.S.
Anita (1977): Mexico
Eloise (1975): Antilles, Northwest Florida, Alabama
Fifi (1974): Honduras, Guatemala
Agnes (1972): Florida, Northeast U.S.
Celia (1970): South Texas
Camille (1969): Mississipi
Beulah (1967): Antilles, Mexico, South Texas
Inez (1966): Lesser Antilles, Hispanola, Cuba, Florida Keys, Mexico
Betsy (1965): Bahamas, Southeast Florida, Southeast Louisiana
Dora (1964): Northeast Florida
Cleo (1964): Lesser Antilles, Haiti, Cuba, Southeast Florida
Hilda (1964): Louisiana
Flora (1963): Haiti, Cuba
Hattie (1961): Belize, Guatemala
Carla (1961): Texas
Donna (1960): Bahamas, Florida and Eastern U.S.
Gracie (1959): Bahamas, South Carolina
Audrey (1957): Louisiana, North Texas
Janet (1955): Lesser Antilles, Belize, Mexico
Ione (1955): North Carolina
Diane (1955): Mid-Atlantic U.S, Northeast U.S.
Connie (1955): North Carolina
Hazel (1954): Antilles, North and South Carolina
Edna (1954): Massachusetts
Carol (1954): Northeast U.S.

Watching two waves

By: JeffMasters, 6:44 PM GMT on July 26, 2005

The tropics remain relatively quiet today. Franklin continues to barely struggle along, and a few modest tropical waves are moving across the far Atlantic. One of these waves, located near 9N 42W, shows some promise for development. It lies over farly warm 29C waters and has some favorable upper level winds over it. As long as the wave maintains its current west-northwest motion at 15 mph, it will stay over warm water and have a chance to develop. But as you can see from the SST plot below, any northward deviation to a latitude north of about 11N will bring it over waters less than 27C, which is the minimum temperature needed for tropical storm formation. A second wave near 12N 30W, just southwest of the Cape Verde Islands, showed some increase in convection the past few hours, and looks more promising than the first wave. However, this wave is very close the the cooler water boundary, so any northward component to its motion would dampen its chances of development. The wave is currently moving west at 10 - 15 mph. The GFS model doesn't develop either of these waves into tropical depressions over the next four days.

Dr. Jeff Masters

Blasts of warm air from Franklin and the importance of Gert

By: JeffMasters, 4:13 PM GMT on July 25, 2005

Gert is gone. A seemingly inconsequential minimal tropical storm, Gert may well turn out to be very important. The reason? The NOAA P-3 aircraft and Gulfstream IV jet did a series of intensive research missions on Gert before, during, and after its formation. They captured a unique data set that may shed light on the little-understood process of how a tropical wave becomes a tropical depression. The NOAA aircraft were also in the storm when it did one of those impossible to forecast "reorganizations", where the center jumped 60 miles in the space of a few hours to center itself under a developing area of intense convection. Forecast models now do a reasonable job predicting the track of tropical cyclones, but are lousy at predicting when they will form and when a storm will undergo a major reorganization. NOAA has been investing in more research to try to improve these models, and hopefully the missions into Gert will help.

Franklin continues to head out to sea and struggle against the strong shear trying to rip it apart. Franklin is only a threat to shipping--unless you believe this news item that went out on the news wire yesterday:

Storm to bring high heat to Florida

Miami - Tropical Storm Franklin strengthened as it spun away from the Bahamas on Saturday and moved farther east in the Atlantic, but blasts of warm air from its core were expected to bring extreme heat the Florida peninsula.

This news story was guilty of presenting some incorrect meteorology. True, Tropical Storm Franklin has a warm core, like all hurricanes and tropical storms do. If the center of Franklin moved directly overhead, one might feel a bit of extra heat (which would be the least of your concerns!) However, "blasts of warm air" certainly are not emanatng from the center of Franklin. The warm core stays pretty shielded from the surrounding environment of a tropical cyclone. Since the winds of these storms spiral into the center, there is really no opportunity for the warm air at the core to emanate out in a "warm blast". If a "warm blast" did emanate from the core, the storm would quickly fall apart! What the article should have said is that the counter-clockwise circulation around Franklin is drawing up hot, humid tropical air into Florida.

Looking out over the rest of the tropics, the only item of note is a large, well-organized wave that just moved off the coast of Africa. The GFS model has this wave turning into a tropical storm in a few days and recurving to the northeast in the middle of the Atlantic Ocean. I'll talk more about this wave tomorrow if it still looks impressive. However, the sea surface temperatures in this region are about 26 - 28C, and 27C is considered the minimum needed for tropical storm formation.

Jeff Masters

Gert and Franklin

By: JeffMasters, 6:47 PM GMT on July 24, 2005

Tropical Storm Gert formed last night, marking the earliest hurricane season ever to have seven named storms. The previous record year was 1936, when the seventh storm formed on August 7. Gert has warm water underneath and good outflow above, but not enough room to do much intensification. A look at the latest SST plot for the Gulf of Mexico shows the warm 29 - 30C water in the southern Gulf under Gert, and also the cold water wake of Hurricane Emily.

The winds of slow-moving Category 2 and higher hurricanes often stir up cooler water from deep below the ocean surface, cooling the surface waters in their wake by 1 - 3C or more. However, the winds of Gert are only 40 mph, and not likely to produce a cold water wake of their own. The sudden stoppage of Emily's cold water wake just before the coast of Mexico south of Brownsville is an artifact of the technique used to make the SST map--data from more than one day is combined. The plot says data from 7/19 through 7/21 were used, and Emily hit Mexico on July 20, so undoubtedly the data near the coast where Emily hit came from July 19, before the storm crossed the coast. The reason multiple days are used to generate these composites it that the satellite making the measurement needs cloud-free conditions to be able to measure the sea surface temperature. The area near the coast of Mexico was no doubt cloud covered on July 20 and 21, so data from July 19 was used. The reason no cold water wake is seen from where Emily approached the Yucatan as a Category 4 hurricane is probably because the storm was moving too quickly to stir up much cold water from down deep. Emily's forward speed was 20 mph then, and slowed down to zero when it approached Brownsville.

Turning our attention to Tropical Storm Franklin, we see a classic example of a sheared system. The low-level center of rotation is almost completely exposed, with just one glob of thunderstorms clinging to the storm's south side. Strong upper level winds blowing from the northwest are ripping away any convection that tries to fire up on the north side of Franklin. The shear is expected to continue for at least the next day, and Franklin should continue heading out to sea and probably weaken further.

Out in the rest of the tropics, nothing eye-catching is happening today, so we may be in for a quiet week for a change!

Jeff Masters

So long Franklin, hello Gert

By: JeffMasters, 6:50 PM GMT on July 23, 2005

Franklin is maintaining itself as a small tropical storm just below hurricane strength. The latest Hurricane Hunter center fixes at 11am and 1:15pm EDT found central pressures of 1002 and 1003 mb, respectively. Maximum winds remained just below hurricane force on both penetrations, and the storm is continuing its NE motion out to sea. The trough that is steering it out to sea may also begin shearing the storm and weakening it 1 - 2 days from now. As NHC hurricane specialist Dr. James Franklin noted in his 5am discussion today, "It is quite possible that little or nothing will be left of Franklin..the storm, not the 2 - 3 days." For now, there is no threat to land from Franklin, and Dr. Franklin will have to wait until his namesake storm's name gets recycled six years from now to get a major hurricane named Franklin.

The tropical wave that crossed the Yucatan last night was slow to develop today, and the Hurricane Hunter mission scheduled to investigate was cancelled. However, the wave has now developed a circulation center in the far southern Bay of Campeche in the Gulf of Mexico, near 19N. Deep convection has increased around this circulation center, especially to the southeast. Upper level winds continue to be favorable for development, and it is likely that Tropical Depression 7 will exist by 5am Sunday. The storm doesn't have much room to maneuver in the Bay, and will probably come ashore on the Mexican coast Monday between Veracruz and Tampico before it has a chance to become a hurricane.

Looking out over the far tropical Atlantic, the disturbance that I discussed yesterday that was approaching Venezuela is now gone, destroyed by interaction with South America. The ITCZ--the zone of deep convective storms that forms where the northeasterly trade winds from the Northern Hemisphere collide with the southeasterly trade winds from the Southern Hemisphere--continues to be very active for this time of year, and the image above shows a large tropical wave in the center of the ocean we may want to watch over the next few days. The GFS computer model suggests that wind shear is now too high to allow development of this wave, but once the wave approaches the Bahamas next Saturday, wind shear might lessen. However, my guess is that the large amount of dry air in the tropics right now associated with the Saharan dust we see on the image will act to discourage any tropical storm formation from this wave.

Dr. Jeff Masters

Franklin, and 3 other tropical waves

By: JeffMasters, 7:54 PM GMT on July 22, 2005

I don't have much to add on Franklin; it is gradually strengthening and beginning to resemble a real tropical storm as it moves away from the shear that was hurting it earlier today. It's still anyone's guess where Franklin will go, and I won't speculate on this more until later. It is interesting to watch the storm's progress on Melbourne Florida's long range radar.

The wave in the Caribbean that was shearing Franklin is now moving over the Yucatan, and appears primed to develop. Only the presence of the Yucatan is keeping it from developing right now, and once it moves into the Gulf tomorrow, I believe we will have another tropical depression.

A small disturbance at 10N 53W has been attracting the attention of several of the people posting comments. This tropical wave has several things going for it--a decent upper-level anitcyclone on top, low wind shear overhead (5 - 10 kt), and warm ocean waters ahead of it. The wave has one big negative--the steering flow is going to carry it into Venezuela. The steering flow does bend more WNW once the disturbance reaches South America, so it is possible that the wave could gain enough latitude to not be totally destroyed by interaction with land. The surface wind field under the disturbance is not well-developed--the QuikSCAT winds show a uniform east find flow under the disturbance, with not much of a hint of a wind shift associated with it. It is possible that this wave could develop into a tropical depression in two days or so, but I think the interaction with South America will likely prevent that from happening.

A tropical wave in the middle of the Atlantic at 11N 35W has some promise; it is further north and less likely to interact with South America. Just north of that tropical wave is a huge low pressure area loaded with African dust. This low has so much dry air and dust in it, that convection has been able to develop in association with it. It is not expected to develop into a tropical depression. This is an unusually large low pressure system for this part of the Atlantic, and will sharply reduce visibilites in the Caribbean islands over the next week when it blows in with its load of Saharan dust. One can see the greyish load of African dust it carries covering nearly half of the tropical Atlantic between the Lesser Antilles and Africa. Residents of the Southeastern U.S. may see the dust from this system color their sunsets late next week.

Jeff Masters

Franklin survives

By: JeffMasters, 12:02 PM GMT on July 22, 2005

Franklin has proved itself to be a survivor. The significant southwesterly shear from the tropical wave in the Caribbean has relaxed a bit as the two systems have moved farther apart--Franklin has moved to the northwest and the Caribbean wave has moved to the west-northwest. There is still some substantial shear from the Caribbean wave, but it should gradually lessen today. However, Franklin has another problem to worry about--the approach of a mid-latitude trough from the west. This trough has plenty of shearing winds of its own, and unless Franklin scoots quickly to the east ahead of the trough, he will be weakened or torn apart by the shear. NHC and the various forecast models all have different ideas of what will happen. The basic scenarios are:

1) Franklin gets picked up by the trough and scooted way out over the open Atlantic, as the GFDL and GFS models are predicting (40% chance).

2) Franklin will follow the official NHC forecast and move to the northeast away from land, then get overtaken by the trough and survive the shearing action of the trough. This would leave Franklin orphaned to await the next trough to sweep it out sea--or potentially come back and threaten the East Coast (30% chance).

3) Franklin will follow the NHC forecast as above, but get destroyed sometime in the next 3 days by shear (20% chance).

4) Franklin will turn due west and move over Florida as a weak tropical storm (9% chance).

It's situations like this one that greatly increase the average hurricane forecast track error. Emily was much easier to predict!

Meanwhile, the tropical wave over the Caribbean continues to look impressive, but is too close to the Yucatan Peninsula to develop much today. On Saturday, when it emerges over the Gulf of Mexico, it has a better chance of becoming a tropical depression. The latest GFS model run calls for it to turn into Tropical Storm Gert and hit the Mexican coast a few hundred miles south of where Emily came ashore.

Jeff Masters

Franklin getting sheared

By: JeffMasters, 1:24 AM GMT on July 22, 2005

Newly-born Franklin is struggling. Recent IR satellite images show a substantial loss of deep convection on all sides of the storm, as strong outflow from the tropical wave in the Caribbean shears Franklin from the southwest side. The tops of the thunderstorms trying to organize around Franklin's center are being torn away by the shear. Since Franklin is still in a fragile formative stage, it is entirely possible the storm will be ripped to shreds in the next few hours, becoming one of the shortest-lived tropical storms on record. The latest Hurricane Hunter report put the central pressure unchanged at 1009 mb, and surface winds about the same as 1 1/2 hours ago. They commented that the center was now poorly defined.

Meanwhile, the tropical wave responsible for shearing Franklin continues to expand its impressive upper level outflow. However, deep convection associated with the wave has decreased in the past few hours, and there is no surface circulation. This wave is still a day or more away from developing into a tropical depression. When and if it does, it could become a very large tropical storm.

Jeff Masters

Here comes Franklin!

By: JeffMasters, 11:05 PM GMT on July 21, 2005

To no one's surprise, the Air Force hurricane hunters found Tropical Depression Six in the Bahama Islands. The 4:30pm EDT report noted maximum winds of 48 kt at the 5,000 foot flight level altitude, which is good enough for tropical storm status, but the Hurricane Center has reasonably decided to wait a few hours to see if the convection continues to build before giving Tropical Depression Six a name. Convection has continued to build the past hour--particularly on the east side and in the 10 mile diameter ring surrounding the center. A new center report came in at 6:40 pm with a pressure fall down to 1009 mb, so I expect with the 8pm intermediate advisory this storm will have a name--Franklin. The sixth named storm of this ridiculous hurricane season.

Upper level outflow is good in all quadrants over TD 6 except the southwest, where winds from the outflow that has formed over the strong tropical wave in the Caribbean are interfering. TD 6 has a cloud-free center apparent on satellite imagery that makes the storm look much stronger than it really is. The Hurricane Hunters noted that the center had a nice circular radar presentation. The storm is over warm 29C water, and there is light wind shear over it, so it would be no surprise if this became a hurricane in two or three days. The track is problematic, since the steering currents are weak and the storm is still in the formative stages. We'll have a better idea where the storm is headed tomorrow morning once the 00Z (8pm EDT) model runs finish.

The tropical wave in the Caribbean southwest of Jamaica is much larger than TD 6. QuikSCAT
from this area show tropical storm force winds, but no evidence of a closed circulation. The wind shear over the wave is expected to relax over the next two days, and both the Hurricane Center and the GFS model point to the possibility that this may become Tropical Storm Gert once it crosses into the Gulf of Mexico Saturday. The GFS model keeps the storm moving WNW and into the Mexican coast on Sunday, south of where Emily made landfall.

Once again, we are having trouble with the blogging software, my previous entry got wiped out. Please bear with us as we solidify the blogging software over the next few days.

Dr. Jeff Masters

After Emily, what next?

By: JeffMasters, 8:07 PM GMT on July 20, 2005

A strong tropical wave is kicking up showers and thunderstorms over Hispanolia and the waters to the north of the island. This wave has some decent deep convection, but no signs of a circulation yet. It is moving WNW towards the Bahamas at about 15 mph, and could become a tropical depression Thursday.

The wave is currently in an area of relatively high shear; the University of Wisconsin's Wind shear analysis from 2pm EDT today (18 GMT) shows an area of 20 knots of shear over the wave. The visible satellite loop shows this shear is acting to rip away the high level cirrus clouds from the tropical wave and blow them to the east.

Lower shear values, 5-10 knots, lie ahead of the wave, so it is possible it will develop into a tropical depression Thursday as it moves into the Bahamas. A Hurricane Hunter airplane will investigate the wave then, if neccessary. Today's 12Z run of the GFS model takes the wave and develops it into a tropical depression by Friday. The depression then weakens and recurves out to sea past North Carolina on Saturday, when a short wave trough and associated cold front move off the East Coast. At this time, the tropical wave does not appear likely to be another Dennis or Emily!

Jeff Masters

Emily makes landfall

By: JeffMasters, 1:15 PM GMT on July 20, 2005

The eye of Hurricane Emily made landfall at 635 am CDT this morning along the northeastern coast of Mexico about 3 miles south of Boca Madre, which is 75 miles south of Brownsville, Texas. Emily had 125 mph winds and a central pressure of 944 mb at landfall, making it a Category 3 hurricane.

Emily managed to hold together and not weaken after yesterday's rapid intensification cycle. I had speculated that the slow movement of the hurricane would stir up cooler waters and cause weakening, and that the cooler waters next to the coast might also weaken the storm. That did not happen, apparently since the other environmental factors (weak wind shear, good upper level outflow) were strong enough to overcome the cooler waters. Mexico was unfortunate to have the storm slow down and make landfall at peak intensity. The slow motion of the storm means that the coast will be exposed to a long period of high water and battering waves. However, this portion of the coast is sparsely populated. Browsville is just north of the area of hurricane force winds, but the coastal areas will take a severe pounding from Emily's storm surge. The rains of Emily, expected to bring 2 - 4 inches to South Texas, will be most welcome, as this part of Texas is under extreme drought.

Emily was undergoing a eyewall replacement cycle at landfall. If one looks at the last VORTEX report from the Hurricane Hunters, one sees the item: "M. CO15-50". This means concentric eyewalls, with the inner eyewall 15 nautical miles in diameter and the outer eyewall 50 nautical miles in diameter. This is the situation that happened several times during the course of both Emily's and Dennis' lives. As a hurricane intensifies and spins tighter and tighter, the eyewall contracts until it is no longer stable and collapses, and a new outer eyewall takes over. I've annotated a radar image below to show the concentric eyewalls of Emily at landfall.

The Brownsville 248 nm mile range radar will be interesting to watch today as Emily moves inland and the eyewalls collapse.

Dr. Jeff Masters

What is Emily doing?

By: JeffMasters, 4:07 PM GMT on July 18, 2005

Posted: 8:50pm EDT Tue July 19
OK, I give up trying to predict what Emily is going to do, I'm just going to watch. Brownsville 248 nm mile range radar shows that Emily has essentially stalled the past 75 minutes. The 7:18pm recon flight showed that the central pressure had risen 6 mb to 948 mb, and saw no increase in flight level winds. With the storm sitting in place, lots of cold water is going to upwell beneath her and make it difficult to intensify further. In fact, the eye appears less distinct than two hours ago, and is filling with clouds. However, a very impressive circular Cirrus Dense Overcast has formed over the hurricane, and the overall banding and outflow still look impressive. Once the hurricane starts moving again away from its cold pool it kicked up underneath itself, it could start intensifying again. What's next, Emily??

As many of you noticed, we've had some problems with my blog disappearing today. The software for this is still in its experimental stages, and has been put to the test today! It seems we sometimes have problems when multiple comments are posted simultaneously. Bear with us, we'll try to keep things working while we craft a permanent fix. Expect to see many improvements in the blog interface over the next few weeks, the code is still under heavy development.

Dr. Jeff Masters

Posted: 4:50pm EDT Tue July 19
I should know better than to doubt this hurricane's abilty to bounce back from adversity! Emily's pressure has dropped 13 mb the past 3 1/2 hours, and is now a 959 mb storm. The winds are still at 95 mph or so, and will take a few hours for Emily to adjust to the new pressure. The satellite presentation and pressure both point towards a Category 3 hurricane, and I imagine the surface winds will be close to 115 mph (minimal Category 3 status) by this evening. The track is doing some major wobbles as the storm reorganizes and deepens, but appears to have a more westward bend. The Hurricane Center is doing the proper conservative thing by advertising a continued WNW motion toward the Texas/Mexico border until the westward turn becomes more obvious.

The hurricane is impressive to watch on the Brownsville 248 nm mile range radar.

Jeff Masters

Emily turning west, strengthening

By: JeffMasters, 2:01 PM GMT on July 18, 2005

The 8:44am Hurricane Hunter eye report confirms what I've been seeing in satellite imagery this morning--Emily has assumed more of a westward motion, which may be the beginning of the long-forecasted turn to the west the forecast models have been predicting. It could also be a temporary wobble, so we'll have to watch Emily the next few hours. If the westward turn is happening, Emily will likely come ashore 60 - 120 miles south of the Texas/Mexico border. Since hurricane force winds extend out only 40 miles from the center, it is unlikely Texas will see hurricane force winds from Emily.

The central pressure dropped another 2 mb to 975 mb the past 90 minutes, and the eye shrunk from an oval 30x45 miles to a circular one 25 miles in diameter. The eye is starting to look distinct on visible satellite images, and the dry air that was disrupting the storm yesterday is mostly gone. Although the Hurricane Hunters did not measure any increase in winds, it is clear that Emily is strengthening, and should be a Category 2 hurricane this afternoon. With landfall expected at 3am Wednesday, it is unlikely Emily will make it to Category 3 status, though--there is not enough time. In addition, she may start interacting cooler water near the coast that will inhibit intensification.

It is interesting to compare Emily to the last bad hurricane to strike Brownsville--Hurricane Beulah, in 1967. Like Emily, Beulah crossed the Yucatan Peninsula and emerged into the Gulf of Mexico as a Category 1 hurricane. But unlike Emily, Beulah was a September storm, and had much warmer water to draw energy from. Beulah was also moving much slower, about 10 mph, which gave it more time to reorganize. After two days over the Gulf of Mexico, Beulah had transformed into a Category 5 hurricane with 160 mph winds and a central pressure of 923 mb. Fortunately, Beulah weakened just before landafll into a Category 3 hurricane with 130 mph winds. Still, a 10-foot storm surge pushed up on the coast near Brownsville, and rainfall amounts of up to 30 inches caused major flooding. Ten deaths were atrributed to the storm, most of them in the 95 tornadoes Beulah spawned. Damage in year 2000 dollars was $1.1 billion.

Image credit: NOAA Photo Library

Brownsville is fortunate the westward turn of Emily is starting to happen--and that it is just July, and that Emily has been moving quickly at 15 - 20 mph over the Gulf of Mexico. Otherwise, Brownsville may well have had another Beulah.

Dr. Jeff Masters

Emily strengthening again

By: JeffMasters, 11:07 PM EDT on July 18, 2005

Posted: 10pm EDT Monday July 17
Emily is slowly strengthening. Latest recon at 9:22 pm from the Hurricane Hunters found the pressure down one mb to 983 mb, surface winds of at least 90 mph, and a good radar presentation of the eyewall. The eyewall was open to the SW, however.

The satellite images also show an improved organization, but also that Emily is still pulling in dry air from the Yucatan. In a few more hours, Emily will move far enough away from the Yucatan so that more significant strenthening can occur. We'll have a Category 2 storm by morning.

As far as the track forecast goes, there is a trough of low pressure pulling Emily a little more northward than yesterday's track; she is now moving at about 300 degrees. However, the cold front attached to the trough just cleared Michigan, bringing heavy thunderstorms here (and FINALLY clearing out the remains of Hurricane Dennis!) This trough and associated cold front are rapidly headed east, and by morning should lessen its pull on Emily. I expect a more westward track tomorrow, as the models and NHC are predicting. Texas should miss a direct hit by Emily.

It's amazing to watch the weather here in Michigan and see connections to a hurricane far away in the tropics. The weather everyone experiences is interconnected and influences what happens to the weather everywhere else. Similarly, for those of you who post to this blog, keep in mind that what you say and think influences what the other readers think and do, so please keep it constructive. It's been great reading everyone's input, keep the comments coming.

Jeff Masters

Emily churning through Gulf of Mexico

By: JeffMasters, 6:44 PM GMT on July 18, 2005

Posted: 2pm EDT Monday July 17
Emily is now a Category 1 hurricane. The 1:22pm EDT Hurricane Hunter mission found a central pressure of 984 mb and peak winds at 10,000 feet on the NE side of 89 mph, which would make Emily's surface winds about 75 mph. Satellite imagery shows a large area of dry air spiraling north from the Yucatan Peninsula and wrapping into the center of the hurricane. This dry air is severely weakening Emily. The storm has a more ragged appearance than when it moved off the coast at 9am, and the lack of convection on the south side has expanded.

Emily has shown great resilience, and may still regain Category 3 status when she moves further away from the Yucatan and stops pulling in so much dry air. However, the kind of disruption of the inner core that appears to be happening usually takes at least a day for a hurricane to recover from, and Emily has only 36 hours before landfall. It is unlikely Emily will be stronger than a Category 2 storm at its next landfall.

Posted: 10am EDT Monday July 17
Emily made landfall at 2am EDT this morning as a Category 4 storm with peak winds of 135 mph and a central pressure of 955 mb. The eye passed just southwest of Cozumel, Mexico, with the northern eyewall passing over Cozumel. No wind, pressure, or damage reports have emerged from Mexico yet, but the 8 - 12 foot storm surge and 135 mph winds must have done tremendous damage.

Emily's eye moved off the coast of Mexico at approximately 9am EDT this morning, after spending just seven hours over the Yucatan Peninsula. The hurricane has survived the crossing fairly intact, as a Category 2 hurricane. The storm looks somewhat lopsided, with a notable lack of cloudiness on the south side where dry air from the Yucatan has been drawn in. However, the eye is still distinct, a decent-looking circular Cirrus Dense Overcast still covers the center of the hurricane, and Emily has exellent-looking spiral banding. This is the look of a hurricane that has been only temporarily disrupted, and will soon begin strengthening. There is plenty of warm water ahead of the hurricane, and low vertical wind shear. I see nothing that will prevent Emily from reaching Category 3 status by tomorrow, perhaps even a strong Category 3.

The track forecast remains pretty much the same, with Mexico expected to receive a second pounding early Wednesday morning when Emily comes ashore about 50 miles south of the Texas border. The median track error the past 10 years for a 36-hour forecast is over 100 miles, so Emily could still hit Texas. However, the NHC has done an great job forecasting this hurricane the past seven days. The five-day forecast issued five days ago put the landfall of Emily as a Category 3 storm directly over Cozumel, and was in error by less than 75 miles. This is a pretty excellent forecast, considering the median error for a 5-day forecast is 310 miles. Since that forecast was issued, the forecast errors for 3-day forecasts have been below 100 miles every day. And with the NOAA jet up in the air sampling Emily's large scale environment each of the past two days, the reliabililty of the current and future forecasts is likely to continue to be excellent. Thus, the chances of Texas getting a direct hit from Emily is less than 25%.

Jamaica was largely spared yesterday, as Emily passed 100 miles south of the island and brought them only tropical storm force winds. However, torrential rains caused serious flooding damage and was responsible for sweeping five people to their deaths when they drove past a closed road blockade and were swept over a cliff by floodwaters.

The Cayman Islands, which Emily missed by only 85 miles, also escaped serious damage. As reported by WunderBlogger CaymanMike:, "Wow! Grand Cayman and the Sister Islands made it through our brush with Emily with nothing more than some gusty tropical storm force winds and some heavy rains. The official word from the government is that the power stayed on over the island, the airport has reopened and no major damage is reported."

Emily powers towards Cozumel

By: JeffMasters, 6:12 PM GMT on July 17, 2005

Posted: 2pm EDT July 17
The 1:15pm EDT Hurricane Hunter report indicated the winds and pressure inside Emily had not changed much. However, the report stated: "Very strong convection with hail outbound thru north eyewall." As a former hurricane hunter, I can speculate on a more detailed version of what happened:

"As our C-130 airplane crossed out of the eye into the north eyewall, the plane hit updrafts and downdrafts of 30 - 40 mph and the turbulence severe enough to throw loose objects around the cabin. The clattering sound of hail on the metal skin of the airplane was loud enough to make your ears ring, and the plane will probably need a new paint job after this ride."

Hail is rare in hurricanes, due to their warm nature. Hail can has cut short several Hurricane Hunter missions in the past--the hail damages engines and instruments, and will strip the paint off the wings. And you can bet if they're mentioning "very strong convection", they're probably getting accelerations of 2 - 3 g's in severe turbulence. The Hurricane Hunters are definitely earning their money today.

Jeff Masters

Posted: 10:30am Sunday July 17
Hurricane Emily is a little weaker this morning, after briefly flirting with Category 5 status last night. The National Hurricane Center never officially upgraded it to a Cat 5, but noted that about 3 GMT (11pm EDT), when Emily had its lowest pressure of 929 mb, it may have briefly attained Category 5 status. The 10am EDT Hurricane Hunter flight found a minimum pressure of 946 mb, up 18 mb from last night. The winds have fallen some, from 155 mph to 150 mph. The eye is no longer as distinct, the Central Dense Overcast (CDO) is not circular, and upper-level outflow on the SW side looks restricted. Emily is undergoing an eyewall replacement cycle, and it appears that this has also made the storm more vulnerable to some shearing. As Steve Gregory noted in his blog, there is more shear than one typically finds over a major hurricane right now--10 knots.

Emily will probably not have time to make it to Category 5, if the last eyewall replacement cycle it went through is any indication. When that cycle started, Emily's pressure rose for about 8 hours, leveled off for 4 hours, then started falling again. A full 24 hours elapsed before she regained her former intensity. The current cycle began at about 11pm EDT, and it appear to be following a similar trend. Emily's pressure rose for 8 hours, and has leveled off the past four hours. Satellite images from the past hour show some improved organization, and re-intensification is probably starting to occur. If it again takes a full 24 hours for Emily to regain her previous strength, she may approach Cat 5 again late tonight. However, Emily will be close to landfall at midnight tonight, and will begin pulling in dry air off of the Yucatan Peninsula late this afternoon. This may disrupt the hurricane enough to prevent it from reaching Category 5. I expect Emily will hit Mexico tonight as a strong Category 4 hurricane.

Emily will hit the resort towns of Cozumel and Cancun hard. When Hurricane Gilbert hit this area in 1988 as a Category 5 storm with 170 mph winds, it took the 125-foot Cuban ship Portachernera and cast it up on the beach at Cancun, where it remained for months.

Image credit:The St. Petersburg Times

Damage from Gilbert to Cozumel alone was $80 million. Damage from Emily will probably be much higher, even though is it a much smaller storm and not as strong. The reason is because the Cancun/Cozumel resort areas had only 8,000 hotel rooms back in 1988, but now have over 50,000. A tremendous amount of development has occurred in the past 17 years. A mass evacuation of the tourists in the area is currently underway, and the towering beach front hotels will stand vacant to confront Emily's wind and seas tonight.

After crossing the Yucatan, Emily will emerge into the Gulf of Mexico as a much weakened Category 2 or even Category 1 storm. Emily is relatively small as hurricanes go, and the passage over the Yucatan should severely disrupt her inner core. Waters over the Gulf are warm--about 30C--but the depth of warm waters is not as deep as the western Caribbean. Thus, the total heat energy available to the storm is probably not enough to support a Category 4 hurricane. I expect Emily will make its second landfall south of the Texas/Mexican border as a Category 2 hurricane. With this intensity, and if the current track forecast verifies, Brownsville would only receive tropical storm force winds. As usual, it must be emphasized that a hurricane's intensity is extremely hard to predict, and Emily could easily be a Category 1 or Category 3 hurricane at its second landfall. Hurricane track forecasts the past 10 years have had a median error of 200 miles for a 72-hour forecast. The official NHC 72-hour forecast puts the landfall point about 100 miles south of Brownsville. So, a landfall 100 miles north of Brownsville--or 300 miles south of Brownsville--should not come as a surprise.

One more note--I do read all of the comments posted, and answer the ones I can do quickly. In many cases, I don't know the answer, or need to perform fair bit of research to confirm my knowledge, so I am unable to post as many follow-ups as I'd like. Last night, I was unable to post from my home up here near Ann Arbor, Michigan. A thunderstorm spawned from the remnants of Hurricane Dennis knocked out power to my neighborhood for 12 hours!

Dr. Jeff Masters

Emily whips into Windward Islands

By: JeffMasters, 12:30 PM GMT on July 14, 2005

Posted: 8:00pm EDT Wednesday July 13 2005
Emily is not struggling anymore, and is finally beginning to resemble a hurricane. The storm is more symmetric now, although smaller in areal extent than before. There is much more deep convection surrounding the center, and the pressure measured by the 8pm EDT Hurricane Hunter flight was 1000mb, down from 1003 mb earlier this afternoon. Emily is likely to be a hurricane tomorrow.

Winds have peaked in Barbados, reaching a sustained 43 mph at 2pm EDT, and were still blowing 35 mph last hour. Winds in Tobago, which will receive the heaviest blow from Emily, were 23 mph at 4pm EDT, and will continue to rise as Emily passes just north of the island. Emily will pass 50 or so miles south of Grenada early tomorrow morning and probably rake the island with winds up to 65 mph. They will take some modest damage, but will be relieved to escape what seemed a few days ago like another hit from a serious hurricane!

Dr. Jeff Masters

Posted: 2:15pm EDT Wednesday July 13 2005
Emily is still struggling. The last Hurricane Hunters mission into the center found the central pressure had returned to 1003 mb, after rising by 2 mb, to 1005 mb. No increase in winds was found. Satellite imagery shows a large band of intense thunderstorm to the northwest beginning to break away from the center, and it appears that the areal coverage of the circulation of the storm is shrinking. The low level center is more than 2/3 exposed. However, the burst of deep convection occurring near the center and to the southeast indicates that Emily is still a vigorous tropical storm.

I believe we will see a much smaller system emerge into Caribbean tomorrow. This is probably due in part to interaction with the South American land mass, the bane of tropical storms entering this part of the ocean.

What will happen next? I give four possibilities:

1) Emily will continue to struggle, pass too close to South America, and die in the Southeast Caribbean, like over 50% of all tropical storms do. (10% chance)

2) Emily will shake off it troubles and become a large Category 1 hurricane by tomorrow. (10% chance).

3) Emily will stay a tropical storm, and eventually make landfall in Central America as a tropical storm (5% chance).

4) Emily will become reorganize today into a small but intensifying storm, and become a hurricane one to three days from now (70% chance).

If Emily becomes a small hurricane, it is likely to follow a more southern course than if it turns in a big hurricane.

Posted: 9am EDT Wednesday July 11 2005

The main outer spiral band of Emily is now passing through Barbados, bringing heavy rain and tropical storm force winds to the island. However, the main force of the storm will be felt further south later today, as Emily passes near Tobago and Grenada.

The first Hurricane Hunter aircraft made it to the center at 8am, and found Emily still in its organizing stages. The central pressure was 1003mb, and the strongest surface winds observed were about 50-55 mph in the northwest quadrant. NHC was estimating peak winds of 60 mph, and the Hurricane Hunters may still find that when they sample the stronger south side of the storm.

The satellite appearance of the storm has a ragged, assymetrical appearance. There is not much thunderstorm activity on the northeast side, possibly signifying that the storm is trying to overcome some dry air in that region. It is likely that it will take Emily at least 12 hours to get its act together and become a hurricane--if it strengthens at all today. In yesterday's blog, I explained that Emily is approaching the SE Caribbean, which is notoriously hostile towards developing tropical storms. I wouldn't be surprised if it took another 36 hours before Emily makes it to hurricane strength.

Emily's lack of organization is good news for the southern Windward Islands, which were hard-hit by Hurricane Ivan in September 2004. Hurricanes are uncommon here; only two hurricanes have crossed through the Windward Islands south of Barbados (13 North Latitude) in the past 50 years. Both hurricanes were notorious villains. One was Ivan. The other was Hurricane Janet (1955), a Category 5 monster, killed over 600 people in Mexico, Belize, and the Caribbean islands. Janet was the only Atlantic hurricane to ever claim a Hurricane Hunter aircraft.

Most of the Windward Islands in Ivan's path suffered modest damage. In Barbados, Hurricane Ivan killed one person, destroyed more than 176 homes, and damaged at least 200 more. Most coastal roads were severely damaged due to erosion caused by the storm surge and wave action. Barbados suffered an island-wide power outage. In St. Vincent and the Grenadines, Ivan damaged 50 homes and washed 2 homes into the seas. More than two-thirds of residents lost power. Tobago suffered 45 buildings damaged, and one death. The tourist industries on all of these islands has fully recovered.

The tiny island nation of Grenada suffered the cruelest blow of any country in the 2004 hurricane season. Ivan's center passed 7 miles south-southwest of the island as a strong Category 3 hurricane with 125 mph winds. The eyewall winds raked the southern portion of the island, killing 39 of the 90,000 residents, and damaging or destroying 14,000 homes--90% of all the buildings on the island. Grenada suffered about $3 billion in damage--over twice their GDP, perhaps setting a modern record for the greatest natural disaster damage suffered by a nation relative to GDP. For comparison, the damage done to Honduras by Hurricane Mitch in 1999 was about 60% of their GDP, and Sri Lanka suffered a loss of about 8% of their GDP due to the 2004 tsunami.

The economy of Grenada will take many years to recover. International aid has totaled as respectable $150 million, but is far short of what is needed. Tourism and agriculture, the two main businesses on the island, were both severely impacted. The country was the world's second-largest producer of nutmeg, after Indonesia. About 70% of this crop was wiped out by Ivan, and will take 7 to 10 years to regrow. Many hotels and restaurants are still under reconstruction, and the island is accomodating far fewer tourists than before the hurricane. Fortunately, a new cruise ship terminal built shortly before the hurricane was not damaged, so the island has been able to attract cruise ships. The island is one year into a planned three-year, $1.2 billion reconstruction program, and it will be at least two years before the Grenada tourist business returns to it pre-Ivan levels. The reconstruction is being done with far superior building codes to prevent a future hurricane from causing such devastation. One assessment found that the simple addition of $75 hurricane straps to anchor roofs would have vastly reduced the number of buildings that were affected. Most of the buildings damaged or destroyed occurred because the roofs peeled off from the building.

I'll close this blog with a poem written by Dr. Joseph Edmunds, former Ambassador from St. Lucia to the United States:


Ivan's invisible unpredictable evil dance,
Satanic uncontrollable whim unroofing
Stable minds, innocent abodes, all.
Uprooting flora, and fauna, national foundations,
Toils of years of sweat, pain, and national pride.

Helpless we were to your hammering winds.
No holy church of sacred godliness spared
No school of future wisdom could withstand
Deliberate slaughtering demolition of a nation,
No imagined reason for targeted disaster.

But Ivan cannot be greater than our people
Resolved to build again from flattened images.
Our vulnerability exposed by unpardonable acts.
No Ivan can destroy our collective resolute, our will
To rise again to new horizons beyond the present.

Ivan, Grenada is greater than your passing!
New roots to reconstruct, new rooftops to rise,
Foundations stronger than before, our people
Will rebuild with human spirit rejecting your return.
The Isle of Spice more spicy it will be.

Emily steadily intensifying

By: JeffMasters, 11:30 PM GMT on July 12, 2005

Satellite imagery shows that the deep convection at the center of Emily continues to become better organized, nice banding features have developed, and upper-level outflow is steadily improving. Emily is advancing over warmer and warmer waters, and the upper-level winds ahead of it look very favorable for intensification. NHC brings Emily up to a Category 3 in three days' time, and I cautiously agree.

Cautiously, because I note that Emily is now moving a little south of due west--it's latitude went from 11.4 to 11.0 North the past six hours. This may have been due to an internal re-organization where the center got sucked underneath where the deepest convection was. The computer forecast models predict that a west to west-northwest motion should begin shortly. However, if Emily's motion continues westward or slightly south of westward, the storm will enter the southeast Caribbean Sea--which historically has been very unfavorable for tropical storms. I've seen countless impressive-looking tropical storms cross through the Windward Islands between 11 and 13 North Latitude, only to weaken or die once they get into the southeastern Caribbean. The reasons for this weakening are not well understood, but one theory is that the presence of the South American land mass to the south cuts off an important source of low-level moisture to developing tropical storms, or entrains dry air into them.

If one looks at the past 20 years of data and finds all hurricanes and tropical storms that crossed into the southeast Caribbean between 11 and 13 North Latitude, here's what one finds:

Two tropical storms that weaken, but later regain their strength:
Lili (2002)
Chantal (2001)

Six tropical storms that die:
Jerry (2001)
Earl (2004)
Joyce (2000)
Arthur (1990)
Isaac (1988)
Danielle (1986)

Two tropical storms that intensify into hurricanes:
Joan (1988)
Emily (1987)

One hurricane that intensifies:
Ivan (2004)

So, in the past 20 years, over 70% of the tropical storms and hurricanes that have crossed into the southeastern Caribbean have died or weakened. But this is the hurricane season of 2005. The normal rules do not apply. Or in the words of NHC hurricane forecaster Dr. James Franklin in today's 5pm discussion, "So far...the 2005 hurricane season seems to have little interest in climatology."

I predict Emily will follow it's namesake storm, Emily of 1987, and continue to intensify once it crosses the Windward Islands into the southeastern Caribbean.

Dr. Jeff Masters

Goodbye, Dennis, Hello Emily!

By: JeffMasters, 5:20 PM GMT on July 11, 2005

The tropical wave that spun off the coast of Africa last week has acquired enough deep convection to be classified as Tropical Depression Five. I've been trying hard to ignore this one the past few days, because tropical waves in July NEVER develop into tropical storms so far out over the Atlantic, DUH! Well, DUH! This is the hurricane season of 2005, and Hurricane Dennis has already shown we need to re-write the rules. A check of the Historical Track Chart for this area shows only four July tropical depressions have formed so far out, and none of these ever made it to hurricane status. So ordinarily, I would say that this storm is probably nothing to worry about; conditions are marginal because sea surface temperatures are fairly cool over the mid-Atlantic. I've seen tropical depressions like this one fizzle and die many times. But I've learned my lesson. This is the hurricane season of 2005--and I fully expect this storm (soon to be named Emily) will become another major hurricane that will threaten the Caribbean and U.S. That's a pretty bold statement for a mere tropical depression in July way out over the open Atlantic, and statistically, the odds of me being correct are probably less than 20%. I hope the statistics are right, and I am wrong. But this is the hurricane season of 2005. The normal rules do not apply.

Where will TD 5 go? Well, a check of the Forecast Verification Chart for Hurricane Dennis reveals that the Navy's NOGAPS model was the best performer. The official NHC forecast was also quite good. The NOGAPS model (and not coincidentally, the official NHC forecast) both bring TD 5 into the central Caribbean. Its way too easy to speculate where the storm will hit land, but I've already been telling my friends who have travel plans to the Caribbean this week to rethink them.

Dennis turned out to be an average major hurricane for Florida, thanks to the sudden weakening that occurred in the few hours prior to landfall. Sudden weakening has afflicted the past three Category 4 hurricanes to threaten the Gulf Coast--Hurricane Opal (1995), Hurricane Ivan, and now Dennis. The reasons for this are probably due to the colder water that typically lies near shore, and the entrainment of dry air from the steering trough to the west. Luck is also an important factor--hurricanes go through natural cycles of intensification called eyewall replacement cycles, and we were lucky Dennis finished its intensification cycle 12 hours before hitting land. This luck does not always hold, as we saw when Hurricane Camille hit the same area of coast at the peak of it intensification cycle.

By coming ashore in a relatively unpopulated beach area, Dennis' damage total will have a tough time catching up to Ivan's $13 billion dollar price tag or Charley's $14 billion. Preliminary estimates peg the damage at $2 - $10 billion, still worthy of a place on the list of the most damaging hurricanes of all-time. Once again, Mobile and New Orleans got very lucky--just a small shift in course could have brought the core of this powerful hurricane over either city, causing incredible damage. One wonders how much longer the Big Easy can escape the Big One; the stretch of coast just to its west has seen two major hurricanes and two strong tropical storms (Arlene and Cindy) in the past year alone.

One also has to wonder about the location of the past four major hurricanes--Ivan and Dennis followed almost identical paths, as did Frances and Jeanne on Florida's east coast in 2004. If I lived in Punta Gorda, where Charley hit last year, I'd be a little nervous watching Tropical Depression Five east of Barbados, wondering if a repeat Charley hurricane might be in the works! This is VERY unlikely, though; direct strikes from major hurricanes are extemely rare for the Gulf Coast of Florida south of the Panhandle. Hurricane Donna (1960) and Hurricane Easy (1950) were the last major hurricanes before Charley.

Dr. Jeff Masters

Dennis moving inland

By: JeffMasters, 12:52 AM GMT on July 11, 2005

Posted: 8pm EDT Sunday July 10

Here's the official word from NHC:

Radar observations indicate that Hurricane Dennis made landfall at 225 PM CDT on Santa Rosa Island between Navarre Beach and Pensacola Beach Florida. Data from the stepped frequency microwave radiometer on board the NOAA hurricane hunter aircraft, as well as flight-level observations from NOAA and Air Force Reserve aircraft indicate that the landfall intensity of Dennis was 115 to 120 mph--a Category 3 on the Saffir-Simpson hurricane scale.

And my comments:
Dennis is still a serious hurricane. A storm surge of 9-10 feet was reported up to 175 miles east of where Dennis made landfall, in the coastal areas just south of Talahassee. Major storm surge flooding is still occurring all along the Florida Panhandle. Water has pushed across Route 98 near Apalachicola and there has been structural damage there similar to what was observed in 1985 with hurricanes Kate and Elena. Saint Marks, Florida--200 miles east of Pensacola--is flooded. Inland flooding worse than Ivan's is occurring throughout Alabama in Florida in areas soaked last week by Tropical Storm Cindy with six inches of rain. Already, Dennis has dumped an addtional 4-8 inches. There have been several reports of tornadoes in both Alabama and Florida, and these tornadoes could very well turn out to be the major killers for this storm. Another area of concern is inland flooding over the Tennessee Valley later in the week--model forecasts show Dennis stalling out over southern Illinois, creating a potential serious flooding event there. Dennis will be a menace for many days to come.

Don't even look out east of the Leeward Islands, where a powerful tropical wave is already spinning and gathering some impressive deep convection around it. And don't look at the calendar, which says July 10, and think about what happens two months from now, on September 10--the peak of hurricane season.

Dr. Jeff Masters

Posted: 3pm EDT Sunday July 10
Dennis is finally coming ashore, just east of Pensacola, and about 30 miles east of where Ivan struck. The central pressure measured by the hurricane hunters has risen to 943 mb, and the strongest winds measured at 10,000 feet have fallen considerably. Dennis will probably be classified as Category 3 with 125-130 mph winds at landfall.

The eye has maintained its tiny 8 mile diameter, and the most extreme damage will be confined to a smaller area than Ivan. I wouldn't be surprised to see Dennis carve a channel straight through Santa Rosa Island, the barrier island offshore from Pensacola. The worst storm surge damage will occur in the East Bay of Pensacola Bay, where a storm surge of 15 feet could occur. Extreme wind damage will miss Pensacola's downtown, but will severely impact Milton, a town of 7,000 people just east of Pensacola. Whiting Field Naval Air Station, just 15 miles inland, will also suffer heavy damage.

Posted: 11am EDT Sunday July 10
Dennis finally peaked in intensity. The hurricane hunters found no further drop in pressure, and the winds have eased off a bit to 140 mph. The eye is a very tight 8 miles in diameter, which a hurricane cannot maintain for very long. This eyewall could start to collapse in the next few hours, which would probably reduce the peak winds at landfall down into the Cat 3 range. Add to that the fact that Dennis is now travelling over cooler 29 - 30C water, and I arrive at the conclusion that this storm will hit as a strong Cat 3/weak Cat 4. High tide is around noon today, so Dennis will not be hitting at the worst time possible. It could have been worse--but not much. Mobile looks likely to barely escape (again) having a huge storm surge roll up Mobile Bay, but Pensacola will receive another punishing blow from a major hurricane worse than last year's Ivan.

Posted: 7am EDT Sunday July 10
Latest hurricane recon showed a pressure drop to 931 mb, 1 mb lower than two hours ago. If Dennis comes ashore with that pressure, it would be the 7th most intense hurricane ever to strike the U.S. An additional pressure fall to 927 mb would rank it number four, behind only Camille, the 1935 Labor Day storm, and Andrew.

Dennis still looks on track for a an exact duplicate landfall where Hurricane Ivan hit along the Florida-Alabama border, just west of Pensacola. The storm surge from Dennis will be one the highest ever for the U.S., up to 15 feet in some locations. The all-time record is Hurricane Camilles's 24.6 feet (image credit: NOAA Photo Library). Expect extensive damage to the weakened dunes and beaches, new cuts opened all the way through barrier islands, and of course near-total destruction of all buildings where the 10-15 foot storm surge values occur. The tourist industry will take a very long time to recover in Pensacola.

Posted: 11pm EDT Saturday July 9
Dennis has slowed down its rapid intensification, and is probably near its lowest pressure. The last recco flight found only a 1 mb drop in 1.5 hours, compared to 5 mb over the previous 2.7 hours and 11 mb in the 1.5 hours before that. Dennis is still traversing a warm pool of 32C waters, so may continue to drop in central pressure until about 3am, when it passes into cooler 30C waters. The winds will continue to increase to Category 4 strength until perhaps 6am, peaking out at 145 mph or so. From 3am until landfall, Dennis will be traversing 28 - 30C waters, which are about what it was seeing earlier today near Cuba. At this time, a slow weakening trend may result as it undergoes an eyewall replacement cycle.

If you're thinking of evacuating now, it may be too late. It's better to be riding out the storm at home than caught in a traffic jam on the expressways.

Posted: 9pm EDT Saturday July 9
Dennis continues its impressive intensification; the pressure dropped 16 mb in 3 hours, which matches the rapid deepening seen in Hurricane Charley last year shortly before it made landfall. Dennis's intensification is probably in part due to the fact it is traversing a narrow pool of 32C (90F) water. The eye has shrunk another 2 miles in diameter to 10 miles, and likely will shrink a little more then break apart like it did before hitting Cuba. I expect Dennis's winds will continue to increase to about 145 - 150 mph to bring it in equilibrium with its new pressure.

Dennis continues to break the rules for what is usual for a hurricane. In my previous blog entry, I wrote that it is very unusual for a major hurricane to regain its former intensity after a long crossing over land. However, Dennis is poised to do just that.

Aircraft recon just measured a central pressure of 947 mb at 5:15pm, an 11 mb drop in 90 minutes--a rarely observed rate of intensification. The eyewall shrank from 15 miles in diameter to 12 miles, and the satellite presentation confirms that the storm is undergoing explosive deepening. Dennis will surely be a strong Category 4 storm in about 6 hours, when the winds have time to catch up to the pressure falls, and Category 5 is not out of the question. Satellite imagery shows an outer wind maximum is probably forming, meaning Dennis will enter another eyewall replacement cycle tonight after this phase of explosive deepening is over.

The current track of the storm is more WNW than NW, and is likely a temporary wobble similar to two others this storm has already done. I expect Dennis will shortly resume its previous northwest track. The most recent wobble occurred as the storm was doing its previous rapid intensification cycle just before it hit Cuba. The current wobble is enough to probably spare Panama City the worst of the hurricane, but increases the danger to Mobile. A direct hit by Dennis just west of Mobile could easily challenge Hurricane Andrew as the most expensive hurricane in history. Dennis's storm surge of 15-20 feet would push into Mobile Bay and cause tens of billions in destruction. Even if Dennis hits further east near Pensacola, as I still expect, the damage will surpass Ivan's $13 billion and Charley's $14 billion to make Dennis the second costliest hurricane on record.

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Entry from 10am EDT
Cuba did the U.S. an enormous favor by absorbing Dennis' worst punch. It's pretty rare for a major hurricane to regain its former intensity after a long land crossing, and Dennis has only until Sunday evening to regroup. While I do believe Dennis will reintensify to a Category 3 hurricane-- which will be plenty bad for the storm-weary residents of the Florida Panhandle, Alabama, and Mississippi--a return to the Cat 4 monster that ravaged Cuba is pretty unlikely. A search back into the hurricane archives for similar storms reveals the case of Hurricane Georges, a strong 1998 Category 3 hurricane that smashed the Dominican Republic. After traveling down the length of Cuba, Georges popped off Cuba as a Category 1 hurricane about the same place Dennis did. Gerorges gradually intensified to a borderline Category 2/3 hurricane with a 12-foot storm surge and 110 mph winds before it hit Mississippi, and did about $5 billion in damage to the U.S. mainland. I'm betting Dennis will have a very similar impact.

It takes at least 12-24 hours for a hurricane to re-establish its inner core eyewall structure after a major disruption like Dennis suffered, which doesn't give it much time before landfall. I give Dennis a 10% chance of hitting as a Category 4, 50% as a Category 3, 30% as a Category 2, and 10% as a Category 1 or weaker. As for landfall location, the computer models are now in pretty unanimous agreement about a Mobile/Pensacola landfall, now that the distraction of dealing with the Cuba interaction is over. When the models all come together like this, it's usually a pretty sure bet that landfall will be within 50 miles of the target.

Dennis hits Cuba

By: JeffMasters, 10:29 PM GMT on July 09, 2005

Entry from Friday, July 8
Dennis has come ashore on the south coast of Cuba, and it took one of the worst possible landfall trajectories--a 70-mile long track scraping the coast with its right eyewall. The right eyewall contains the hurricane's strongest winds and highest storm surge, and normally only a 5 to 10 mile section of coast suffers it. Cuba just had 70 miles of coast with some of its prime tourist areas suffer a storm surge of at least 13 feet, and probably 20 feet or higher in many places. Add to this the hurricane's sustained winds of 145 - 150 mph, and the result will be a multi-billion dollar destruction of a key part of the island's economy. Dennis has also made a direct hit on Cienfuegos, a city of 200,000, and is now aiming at the Caribbean's largest city, Havana. The destruction occurring in Cuba from this storm must be truly staggering.

Ham radio reports from Cienfuegos indicate that more than 85% of the power lines were down and extensive damage had occurred to the communications infrastructure. Sustained winds of 99 mph and a wind gust of 149 mph was measured in the city at 1:30pm EDT.

Entry from 10am EDT
Yesterday afternoon, Dennis went through an eyewall replacement cycle where the inner eyewall collapsed, and a new eyewall formed with a diameter of about 20 miles. This ended a period of rapid intensification, and the storm stayed roughly constant in intensity as a minimal Category 4 storm (135 mph, 950 mb).

The 8:30am EDT hurricane hunter flight just found a central pressure of 938 mb and winds at 10,000 feet of 155 mph, which means Dennis has recovered from its eyewall replacement cycle, and is now intensifying again. The eye is a healthy 15 miles in diameter, and it is unlikely that another eyewall replacement cycle will happen before the storm hits Cuba tonight. Cuba will probably see Dennis at its peak--and this could very well mean Category 5.

Dennis is now the most intense June or July hurricane on record, beating out Hurricane Audrey of June 1957, which was a Category 4 storm with 145 mph winds and a central pressure of 946 mb at its peak. Audrey killed 390 people in Texas and Louisiana when it came ashore, making it the sixth most deadly U.S. hurricane on record.

Today will be the worst day in Cuba's modern history. Dennis is a worst-case hurricane following a worst-case path for the island. The storm is already punishing Cuba as it moves parallel to the island, subjecting much of the island to hurricane force winds and rainfall totals of 10 - 15 inches, and destroying much of the rich sugar cane fields and other crops. The situation will get much worse tonight when the storm makes landfall, pushing a storm surge of 20 feet or higher onto a long section of the coast. Dennis will pass near Havana, the most heavily populated part of the island. Although loss of life will be low thanks to Cuba's excellent civil defense system, the destruction of buildings will probably be the worst in Cuba's history. Building collapses are common in Cuba without having hurricane winds battering the cities. Dennis will damage or destroy hundreds of thousands of buildings, leaving a large percentage of Cuba's population homeless. Lack of fresh water and electricity will be serious problems, and Cuba's political stability could well be threatened by the scope of what is likely to be its greatest disaster in modern history.

On that cheerful note, let's talk about the plight of the poor people living in Florida's panhandle, which is likely to bear the brunt of yet another major U.S. landfalling hurricane. Dennis will cross Cuba over a realtively flat section of the island, and be reduced in intensity to only a Category 3 or weak Category 4. Once over the Gulf, some intensification is likely, but the amount remains uncertain. The waters get cooler further north, and since we are still early in July, the depth of warm waters is limited. Dennis may stir up enough cool waters from down deep to limit intensification to a Category 4, or perhaps even reduce it to a Category 2. Dennis looks likely to hit within 50 miles of where last year's Category 3 Hurricane Ivan hit, killing 25 and causing $7 billion in damage. Expect a repeat of this performance, although the exact strength of Dennis at landfall could range between Category 2 and Category 4, and will greatly influence how much damage is done. Key West will likely get hurricane force winds tonight, but miss a direct hit by 40 or so miles. The outer bands of Dennis are already affecting the island; a squall with heavy rain and winds to 30 mph passed through the island at 8:30am. The rest of the west coast of Florida is also likely to miss a direct hit, but still get tropical storm force winds of about 40 mph.

Entry from Thursday, July 7
At 3:55pm EDT, the hurricane hunters sent in an eye report of a central pressure of 957 mb, 1mb higher than the previous hour's report. They also reported the eyewall was beginning to break up, with an elliptical shape 9 x 6 nm, and open to the south. Satellite pictures also show the disintegration of the inner eyewall, and the storm should begin a slow weakening period that will last a day or so. It should maintain Category 3 strength until it hits Cuba. NHC is forecasting Dennis to continue intensifying the next 12 hours, which I believe means the winds will continue to come up into equilibrium with the rapid pressure drop we saw. I wouldn't expect much in the way of pressure falls until tomorrow, when the eyewall can re-establish itself.

Entry from 1 hour ago:
At 2:30pm EDT, the hurricane hunters sent in an eye report of a central pressure of 956 mb--an impressive 6 mb drop in just 70 minutes! The eye diameter was a tiny 9 nm (10.5 miles), and the storm is undergoing the rapid shrinkage of the eye and sudden deepening characteristic of an eyewall replacement cycle. I expect that within a few hours, the winds will respond to the sudden pressure drop, and Dennis will be a major Category 3 hurricane, and may make it to Category 4 status (135 mph winds) before the inner eyewall collapses and the storm starts weakening slightly. Dennis will not reach Category 5 status today, though--the pressure would have to be much lower than 956 mb at the beginning of an eyewall replacement cycle to achieve Category 5 status. Nevertheless, Hurricane Dennis has grown into an impressive Cape Verdes-type hurricane, and will be a serious threat to everything in its path. After blasting Haiti and Jamaica, Dennis's next targets will be the Cayman Islands and Cuba--and then the Florida Keys. Today, I will focus on the Caymans, Cuba, and the Florida Keys. Tomorrow--it's time to talk about the mainland U.S.

Florida emergency management officials have ordered a mandatory visitor and nonresident evacuation for the entire Florida Keys beginning at noon Thursday. At 6 pm, all residents of mobile homes are required to evacuate. The rest of the residents of the Keys have not been ordered to evacuate, but likely will be asked to do so Friday. With only one road out of the Keys, this part of the U.S. has the longest lead evacuation time--a full 72 hours is needed to evactuate the entire island chain. Last year, Hurricane Ivan prompted a mandatory evacuation order as well, and 30,00 - 60,000 of the 80,000 residents of the Keys heeded the order. The Keys escaped serious damage from Ivan, and no doubt many Keys residents will try their luck and ignore the evacuation order for Dennis. Like Jamaica and New Orleans, the Keys have had an inordinate amount of luck dodging direct hits from major hurricanes. I think their luck will hold this time around, too, but one of these days, those residents who ignore the evacuation order will wish they hadn't!

Grand Cayman Island is still years away from recovery from last year's Hurricane Ivan, which brought sustained winds of 150 mph, gusts to 170 mph, and a storm surge of 10 - 12'. 95% of all the buildings on the island were damaged or destroyed. Grand Cayman will likely escape the brunt of Dennis, but its sister islands Little Cayman and Cayman Brac, which lie 150 km to the east-northeast, may feel the storm's full force. Cayman Brac escaped Hurricane Ivan's rampage with minimal damage--winds only reached 50 mph there--but Dennis may bring winds of over 100 mph. Loss of life on Cayman Brac is unlikely, though, since the island's population of 1300 generally takes shelter in a large network of natural caves on the west end of the island that provide ideal hurricane protection. Cayman Brac's reefs--ranked by diving enthusiasts as some of the best in the world--are unlikely to be seriously harmed by Hurricane Dennis, though. Ivan, a much stronger storm, did only minimal damage to the reefs near Grand Cayman Island, and did divers a favor by clearing out old algae deposits and opening up new holes in coral walls for divers to explore.

After whipping the Cayman Islands, Dennis will likey hit western Cuba. This is the same region that was struck by Hurricane Charley on Friday, August 13, 2004 (Fidel Castro's 78th birthday). Charley was a Category 3 storm, with sustained winds of 120 mph and a storm surge of 13 feet when it hit Cuba, passing just 15 miles west of Havana. Charley did over $1 billion in damage to Cuba, and damaged or destroyed over 70,000 buildings. The 13 foot storm surge on the coast south of Havana was particularly devastating. For example, the fishing village of El Cajio on Cuba's south shore lost 290 of its 300 homes to the storm surge.

Charley caused serious problems in Havana and the surrounding areas. 70% of Havana's two million residents had no fresh water four days after the storm, and more than half had no power 2 weeks after the storm. The Cuban government shut down the entire electrical grid in the hours prior to Charley's arrival to prevent damage from power surges and intermittent service, or else the damage to the power grid would have been far worse.

Unfortunately for Cuba, Dennis is likely to bring a replay of the miseries brough by Charley. A storm surge of 12 - 14 feet is likely once again, and since the storm is travelling at more oblique angle to the coast than Charley did, the area of Cuba likely to be seriously affected by hurricane is much greater. Dennis will be another billion dollar hurricane for Cuba, and probably the second most destructive hurricane ever to hit the island, behind 2001's Category 4 Hurricane Michelle, which damaged or destroyed over 110,000 buildings. But thanks to Cuba's phenomenal civil defense plans, loss of life is likely to be low. Only five Cubans died in Hurricane Michelle, and four in Hurricane Charley.

Entry from Wednesday, July 6
Dennis is steadily intensifying, and will likely affect the islands of Hispanolia, Jamaica, and Cuba as a Category 1 or 2 hurricane before coming ashore in the U.S.--who knows where? Since it is way too early to speculate on where in the U.S. Dennis might hit, let's focus on which island will bear the brunt of the storm.

The latest computer model guidance is tightly clustered, bringing Dennis between Jamaica and Hispanolia on Thursday. Dennis could potentially hit either island as a Category 1, 2, or 3 hurricane. Let's consider Jamaica first. In 2004, Category 4 Hurricane Ivan was headed straight for Jamaica, and in the final hours just before landfall, made a sudden jog to the south around the island, largely sparing it from massive destruction. The track looked so suspicious, I suspected at the time that Jamaica somehow deflected the storm by creating some sort of alteration of the steering currents of the hurricane. I couldn't think of a very good mechanism for how this might have happened, though, since Jamaica is a small island, and the tallest mountains on the island are only 7,000 feet high. Steering currents for a hurricane operate at much higher altitudes, centered at an altitude of perhaps 25,000 feet. When I used NOAA's excellent Hurricane Tracking Tool to plot up all Category 2 or higher hurricanes for the past 150 years that passed within 75 miles of Kingston, Jamaica, it revealed that Ivan was the only storm that made a sudden jog around Jamaica, and that in general, hurricanes just ignore the island and blast right over it.

So, don't be surprised if Dennis rips straight across Jamaica like Hurricane Gilbert did in 1988. However, Jamaica is heavily forested and able to handle extreme hurricane rains without major loss of life; furthermore, the hurricane storm surge is usually not a problem, since the storm surge wave can just wrap aorund the island without being forced up on shore. The primary hazard to people are the winds, which easily destroy the tin shacks much of the poor populace live in, but usually don't cause heavy loss of life. A direct hit by Dennis will cause a lot of damage but not much loss of life on Jamaica.

Of greater concern is Haiti. A direct hit by even a Category 1 Hurricane Dennis could easily kill thousands on island, and even a side-swipe could well kill hundreds. The problem on Haiti is that they have chopped down 98.4% of all their trees, leaving the denuded mountains unable to absorb heavy rains. Heavy hurricane rains wash down the mountainsides, sweeping the helpless Haitians to their doom. Last year's Hurricane Jeanne--just a tropical storm when it hit Haiti--killed over 3000 Haitians, making it the 12th most deadly hurricane ever. Dennis' current projected path has it sideswiping Haiti's western tip, which is less populated than the areas of the island that usually suffer extreme devestation, so I am hopeful that Dennis will cause minimal loss of life in Haiti.

Entry from Tuesday, July 5
The newly-formed Tropical Storm Dennis over the eastern Carribbean looks poised to become Hurricane Dennis later this week. The storm has a typical look of a classic Cape Verdes-type hurricane at its formative stages. It has a large circulation covering most of the eastern Caribbeam, plenty of deep convection near the center, spiraling bands of low-level cumulus wrapping into the center, and a decent upper-level outflow pattern of high cirrus clouds. The storm is over warm ocean waters >28C and has a favorable environment with light shear ahead of it. The only strikes against it would seem to be the mountainous terrain of Cuba and Jamaica, plus history--Cape Verdes-type hurricanes are quite rare in July. Dennis is only the 3rd tropical cyclone to form in the eastern Caribbean in July. Despite this history, I will not be surprised if this storm becomes a large and dangerous Cape Verdes-type hurricane later in the week.

In fact, this hurricane season has set the record for the earlist hurricane season with four named storms (records go back to about 1850). The previous record was set in 1959, when there were four named storms by July 7. Does all this activity in June and July portend a record-breaking hurricane season for 2005? Dr. Chris Landsea notes in his excellent Hurricane FAQ that "the overall number of named storms (hurricanes) occurring in June and July (JJ) correlates at an insignificant r = +0.13 (+0.02) versus the whole season activity. In fact, there is a slight negative relationship between early season storms (hurricanes) versus late season (August through November) r = -0.28 (-0.35). Thus, the overall early season activity, be it very active or quite calm, has little bearing on the season as a whole."

Indeed, although four named storms formed by July 7 in 1959, the season turned out to be an ordinary one, with 11 named storms (which is average) and 7 hurricanes (one more than average). However, storms forming early in the season out in the area Dennis formed (south of 22 North Latitude and east of 78 West Longitude) are very often a harbinger of an active hurricane season. For example, take a look at 1933, when a record 21 named storms and 10 hurricanes formed, with four of the five June and July storms forming in this area.

Tropical Storm Cindy

By: JeffMasters, 2:47 PM GMT on July 05, 2005

OK--its got a name, but this one will have no fame. Big brother Dennis is going to steal all the headlines this week. I've been championing Cindy as a beneficial drought-busting tropical storm, but the very real possibility exists that Cindy may dump enough rain over the Centeral Gulf states tomorrow that a direct hit by big brother Dennis next week over the same area would cause much more severe inland flooding problems than it otherwise would.

Dr. Jeff Masters

Entry from Monday, July 4
Tropical Depression Three still looks like its hanging together enough to survive crossing the Yucatan crossing. There is plenty of dry air on the southwest side of the storm, but lots of deep convection on the northeast side, and a large enough circulation that the storm will have plenty of spin to re-energize the inner core convection once the center emerges over water.

As for the Yucatan being a "hurricane killing" traverse, let's look at the stats of those storms the past 10 years that attempted to cross the Yucatan:

Isidore (2002) hit the Yucatan as a Category 3, weakened to a 40 mph tropical storm, then gradually strenthened the next two days before hitting Louisiana as a 65 mph tropical storm.

Keith (2000) hit the Yucatan as a Category 4, weakened to tropical depression, then took 2 days to regain strength in the Gulf after the crossing and hit Mexico south of Brownsville as a Category 1 hurricane.

Katrina (1999) hit the Yucatan as a tropical depression, then died before it made the crossing.

Dolly (1996) hit the Yucatan as a Category 1, weakened to a tropical depression, then stregthened back to a Category 1 hurricane and hit Mexico after re-emerging into the Gulf.

Roxanne (1995) hit the Yucatan as a Category 3 hurricane, weakened to a 65 mph tropical storm, then re-strengthed to a category 1 hurricane once it emerged into the Gulf.

So for these five storms, all were significantly reduced in strength, but only one was actually terminated by its Yucatan crossing. Perhaps we should call the Yucatan "the bane of hurricanes". It is rare indeed that any storm that encounters the Yucatan regains its original strength. TD 3 could very well break this convention if it survives passage today.

Dr. Jeff Masters

Entry from Sunday, July 3
We've got another tropical cyclone in the Atlantic, Tropical Depression Three in the Western Caribbean, continuing our pattern of above-average activity this hurricane season. TD 3 is only the third July tropical depression to form in the Western Caribbean in the past 136 years.

TD 3 has a large circulation envelope, so is likely to survive the crossing over the hurricane-killing Yucatan Peninsula and re-energize over the Gulf of Mexico into Tropical Storm Cindy. Will it make it to hurricane status? It's way too early to speculate, as the storm first has to survive crossing the Yucatan, then reorganize. It typically takes a storm about two days to reorganize once it crosses the Yucatan, which will give Cindy (if it makes it to Cindy-hood) just one more day over the warm Gulf of Mexico waters to intensify before it comes ashore in Texas or Louisiana. In all liklihood, Cindy will be a tropical storm, and be a blessing to drought-parched areas of Texas, Louisiana, and Arkansas.

For a more detailed analysis of TD 3 and of all the happenings in the tropics this hurricane season, check out the blog of Steve Gregory, a former forecaster with the National Weather Service with 30 years experience forecasting tropical weather.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather