Category 6™

Zeta to ring in the New Year

By: JeffMasters, 5:02 PM GMT on December 31, 2005

It's fitting that the unbelievable Hurricane Season of 2005 will only end when the calendar flips a page at midnight tonight, officially ending the most destructive and prolific Atlantic hurricane season on record. When I wrote my first blog of hurricane season on June 8 about Arlene, little did I suspect that I'd be toiling away on New Year's Eve seven months and 27 storms later, talking about Tropical Storm Zeta!

So here we go, the last blog on the Hurricane Season of 2005. Zeta briefly flirted with hurricane status last night, when an eye-like feature developed and a Central Dense Overcast (CDO) feature characteristic of hurricanes formed over the center. This morning, however, shear from powerful westerly winds has disrupted the eyewall and exposed the center. Zeta has deep convection only on its northeast side, and is struggling to hold onto that. Wind shear is about 25 knots and is expected slowly increase over the next two days as the storm tracks slowly westwards, and the shear should be able to tear the storm apart by Tuesday. However, the GFDL model is forecasting that Zeta will overcome this shear and strengthen to hurricane status as it recurves northwards on Monday and Tuesday.

So, it appears likely that we'll ring in the New Year with a tropical storm, the second time that has occurred. In 1954, Hurricane Alice also was around at midnight on New Year's eve, ringing in the new year of 1955. It's interesting to note that there were two storms named Alice in 1954. Alice 1 formed in June of 1954. Alice 2 formed on December 30, and should have been given the name Irene, but was not officially recognized as a tropical cyclone until January 1, 1955, when it was given the name Alice as the first storm of 1955 (they used the same list of names each year back then). When it was discovered during post-storm analysis that the storm had actually formed on December 30, it kept the name Alice, but was designated as part of the 1954 hurricane season. Most reports called this storm Alice 2 in order to avoid confusion with the earlier Alice from 1954.

Happy New Year, everyone, and I'll be back to update the hurricane season of 2006 tomorrow!

Jeff Masters

Zow! It's Zeta!

By: JeffMasters, 4:39 PM GMT on December 30, 2005

The unbelievable Hurricane Season of 2005 has decided to ring in the New Year with a final tropical storm, and a final record. Satellite imagery indicates that an area of low pressure in the eastern Atlantic has developed into Tropical Storm Zeta about 1000 miles south-southwest of the Azores. Zeta is the latest tropical storm on record to form in the Atlantic. The previous record was held by Hurricane Alice of 1954, which also formed on December 30, but earlier in the day than Zeta.

Like its Greek cousins Delta and Epsilon of November, Zeta formed in conditions one would not normally expect a tropical storm to form--sea surface temperatures are only 24 C (2 1/2 degrees below the 26.5 C minimum usually needed), and under wind shear of 20-25 knots (usually, wind shear of 15 knots or less is required.) However, all these storms formed from pre-existing low pressure systems, and these type of systems are more resistant to shear thanks to their well-developed circulations.

Zeta is trapped under a strong ridge of high pressure that will force it to move on a slow westward track for the next three days. A trough of low pressure moving across the central Atlantic may weaken the ridge enough to turn Zeta northwards and recurve it on Monday, but the ridge may be strong enough to insulate Zeta from this trough and keep the storm moving westward through at least five days, when another, stronger trough of low pressure should be able to turn Zeta northwards and dissipate it.

Zeta has an impressive satellite signature today, with good spiral banding and upper-level outflow. There is 20-25 knots of wind shear over the storm, and this shear is expected to increase substatially to 40-50 knots by New Year's Day. This may make Zeta's existence a very short one. The SHIPS intensity model is calling for Zeta to dissipate by January 1. If Zeta can survive past January 1, shear levels are expected to relax, and Zeta could hang around for most of the week. I don't expect Zeta to threaten any land areas, or make it to hurricane strength.

Jeff Masters

Tsunami weather

By: JeffMasters, 8:41 PM GMT on December 28, 2005

Monday marked the one-year anniversary of the great December 26, 2004 Indian Ocean tsunami, which killed over 283,000 people. The earthquake that generated the tsunami was the fourth strongest in the past century, and caused an oscillation of the Earth's surface of about 20-30 cm (8 to 12 in), equivalent to the effect of the tidal forces caused by the Sun and Moon. The shock waves of the earthquake were felt across the planet--even as far away as Oklahoma, where vertical movements of 3 mm (0.12 in) were recorded. The entire Earth's surface is estimated to have moved vertically by up to 1 cm.

What effect did this remarkable event have upon the Earth's weather? According to the Harris' Farmer's Almanac for 2006 (not to be confused with its competitor, the Old Farmer's Almanac), the unique weather of 2005 was largely attributable to the tsunami:

"The fact that the tsunami churned through the water, altering the sea surface temperatures, did have an influence. The unusual water temperatures changed the weather conditions above the water's surface and that, in turn, changed the weather locally, regionally, and even around the globe."

However, an examination of the sea surface temperature imagery from the days immediately following the earthquake shows that the tsunami had very little effect on the ocean temperature. While there was some minor cooling observed within 1 km of the shorelines closest to the earthquake's epicenter, by two days later (Figure 1), sea surface temperatures in the region showed no trace that anything unusual had happened. The impact of the tsunami on sea surface temperatures was less than that of a weak tropical storm! This is because while a tsunami can create tremendous waves and mixing of the water when it crashes ashore, this effect is limited to shallow waters 1 km or less from shore. The tsunami's impact in deep water is very limited. Satellite measurements of the tsunami's passage over the open ocean revealed a maximum wave height of only 50 cm (20 in), which caused very little stirring of the water over the open ocean. There is nothing at all to suggest that this tsunami, or any tsunami in recorded history, has had a significant impact on regional or global weather.

Figure 1.Sea Surface temperatures anomolies one day before and two days after the Dec. 26, 2004 tsunami. The anomalies (the difference between average sea surface temperature and observed temperature) show virtually no change due to the passage of the tsunami waves.

Jeff Masters

Moscow's very white Christmas

By: JeffMasters, 5:42 PM GMT on December 27, 2005

Moscow, Russia had it's third heaviest snowfall since 1879 just before Christmas, when 25 cm (9.8 inches) of snow plastered the city on December 20 - 21. Moscow's biggest snowstorm of all time was December 15 - 16, 1966, when a storm brought 27 cm (10.9 inches) of snow to the city. I was a little surprised to see a city so notorious for its winters has such a modest amount of snow for its record snowfall. But when you look at a map at Moscow's location in the middle of the Eurasian landmass, far from any any sources of warm, moist air that might lead to heavy snows, one can see why. Moscow has a moderately dry climate, averaging 27 inches (69 cm) of precipitation each year. An average of 22 inches (56 cm) of snow falls each December.

Jeff Masters

Winter Weather

Wind-blown reporters

By: JeffMasters, 3:46 PM GMT on December 23, 2005

It's an ingrained part of the media-presented spectacle of hurricane coverage: a wind-blown reporter struggles against stinging rain and buffeting winds to breathlessly deliver his or her dramatic story. It's been an integral part of hurricane reporting ever since Dan Rather first made a name for himself with his dramatic reporting from Galveston's seawall during Hurricane Carla in 1961--the first time that television news did live hurricane coverage. But with several reporters narrowly escaping serious injury during coverage of this year's hurricanes, a backlash against this type of reporting is starting to emerge. I, for one, am tired of seeing reporters foolishly risking their lives for a breathless sound bite. I would far prefer that they do their story from safe shelter. They could stick a long pole with a telephone book on it out into the wind and watch it get shredded for drama! Or chuck frisbees into the wind, or have wind up toys march into the tempest and get blown away, or a host of other creative things. Reporters need not be put at risk!

A December 18 article in the Miami Herald reported on the first case I've heard of where a complaint was filed to OSHA over reporters' safety during hurricane coverage:

WSVN staffers wonder who filed an anonymous complaint against the station with the U.S. Labor Department's Occupational Safety & Health Administration (OSHA) over reporters' safety during hurricane coverage. Luis Santiago, OSHA's area director, confirms the complaint came in Sept. 20 -- a few weeks after Hurricane Katrina.

The allegation: field reporters were exposed to possible injury because they were not provided with safety glasses, face shields, gloves, respiratory protection from flying sand, hard hats and personal flotation devices.

The station's business manager, Diane Jaramillo-Guard, responded "satisfactorily" to OSHA and the case is closed, Santiago says. But, he adds, workers' safety is always of utmost concern. "Management should make very clear to all employees -- no job is so important that you would put yourself in harm's way."

At the upcoming annual meeting of the American Meteorology Society in Atlanta in early February, a special 3-hour communication workshop has been set up to explore this issue, which I hope to attend. Here's the workshop announcement:

Media coverage of land-falling hurricanes has been scrutinized and debated, and even been the subject of humor columns and the op-ed pages. Why are reporters strapped to trees in order to bring viewers images of roofs and street signs hurling through the air or standing ankle deep on the beach talking about dangerous surf and storm surge? Is this just sensational journalism or proving valuable news coverage?

The Fifth Communication Workshop will take a closer look at hurricane coverage from several different perspectives: the broadcast meteorologist who covers the storms from the stations weather studio, the reporter standing on the beach during 75 mph winds, and the executive decision maker who sends the reporter to the beach. If you have a gripe about media coverage during hurricanes or severe weather and want to see better science coverage, this is the time to share your thoughts and insights.

Speakers include Peter Dykstra, executive producer for Science, Technology, Space, Environment, and Weather at CNN; Max Mayfield, director of the National Hurricane Center; Bob Breck, chief meteorologist at WVUE-TV in New Orleans, LA; Greg Agvent, director of planning at CNN; and Terry Connelly, senior vice president/general manager, The Weather Channel Network.

I'll be back next week with some observations on this winter's weather. The climate change blogs will resume after January 1.

Have a great Christmas, everyone!

Jeff Masters

Katrina officially downgraded to a Category 3

By: JeffMasters, 4:08 PM GMT on December 21, 2005

Today is winter solstice--the darkest day of the year--and an appropriate time to revisit America's other darkest day of the year, August 29. The National Hurricane Center (NHC) issued its official Tropical Cyclone Report for Katrina on Tuesday. Katrina officially made landfall as a Category 3 hurricane, not a Category 4. Ground-based and aircraft measurements only support 110 knot winds (127 mph) at Katrina's first landfall near Buras, Louisiana. Katrina weakened only slightly before her second landfall, and was still a Category 3 hurricane with 105 knot (121 mph) winds on the Mississippi coast. The NHC report also stated that the highest sustained winds over metropolitan New Orleans were only of Category 1 or 2 strength, although buildings over 25 stories high may have seen winds a full category higher.

The reason Katrina was originally classified as a Category 4 at landfall was because winds measured by the Hurricane Hunters at flight level (10,000 feet) were 150-155 mph. The normal rule of thumb used to estimate surface winds is a 10% redution from the winds at 10,000 feet. This rule of thumb was applied for the official NHC advisories issued at the time of Katrina's landfall, and made Katrina a Category 4 hurricane with 135-140 mph surface winds. However, detailed analysis of the wind structure of Katrina in data gathered by Doppler radar and dropsondes showed that at landfall, Katrina had its highest winds in an unusually strong band of winds between 2 and 4 km (the flight level of the Hurricane Hunters was about 3 km). Normally, the highest winds in a hurricane are found much lower, near .5 - 2 km. Surface winds measured by dropsondes, surface towers, and the SFMR microwave radiometer on the aircraft all agreed that the surface winds at landfall were no higher than 100 knots (115 mph). NHC adjusted these upwards by 10% to account for the fact that the strongest winds were likely not sampled. The 10% adjustment left Katrina just 5 mph shy of Category 4 status--but still a very potent and deadly major Category 3 hurricane.

The 10% reduction "rule of thumb" was not valid for Katrina at landfall, probably because the storm's convection was weakening at that time. Because momentum transport from aloft to the surface was impaired by the weakening convention, Katrina was less able to carry the strong winds that were aloft down to the surface. Thus, winds at the surface were about 80% of the winds measured at 10,000 feet. Still, NHC does mention that given the uncertainties and large wind field of Katrina, the very tip of the Mississippi Delta near Buras may have received Category 4 winds for a few minutes, and it is possible Katrina really was a Cat 4 at landfall.

Why Katrina weakened at landfall
At peak intensity, Katrina was a Category 5 hurricane with 150 kt (174 mph) winds, but in the 18 hours before landfall weakened to 110 kt (121 mph). This weakening occured as a result of entrainment of dry air into the storm, slightly cooler sea surface temperatures near the coast, and interaction with the land. NHC notes that the relative importance of these three factors cannot be determined without a lot more study, but all 11 hurricanes with pressures less than 973 mb that have hit the Gulf coast the past 20 years have weakened in the 12 hours prior to landfall. Thus, Katrina's weakening should come as no surprise. Note, however, that Hurricane Camille of 1969 did not weaken when it pounded Mississippi as a Category 5 hurricane; perhaps it's small size protected it from substantial land interaction and entrainment of dry air.

Storm surge
To me, the biggest disappointment in the report came in the treatment of Katrina's storm surge. No storm surge data was presented for New Orleans. No mention was made that Katrina, despite its Category 3 strength at landfall, pushed a Category 5 level storm surge to the coast. The report noted that official storm surge measurements were unavailable, due to failure of most of the tide gauges. However, one unofficial storm surge height of 27 feet at the Hancock County Emergency Management Office in Mississippi was mentioned, which would make Katrina's storm surge the highest on record for an Atlantic hurricane. The previous record was Hurricane Camille's 24.7 feet. Any surge above 18 feet is considered a Category 5 level storm surge. I've seen unofficial estimates that the storm surge affecting the eastern side of New Orleans was 18-25 feet high, which is clearly a Category 5 storm surge. Not surprisingly, the levees protecting the east side of the city were overwhelmed and failed in multiple locations. However, observational data and computer modeling indicate that storm surge entering the canals from Lake Pontchartrain reached 9 to 11 feet in the 17th Street Canal and 11 to 12 feet in the London Avenue Canal. The flood walls were 13.5 feet high or higher along much of the two canals and were designed to withstand water rising to 11.5 feet. A Category 3 storm surge is 9-12 feet, so these flood walls failed in a Category 3 level storm surge, even though they were supposedly designed to withstand that type of storm surge.

Katrina officially made landfall at Buras, LA, with a central pressure of 920 mb. This is the third lowest pressure on record for a U.S. landfalling hurricane, surpassed only by the two Category 5 hurricane to hit the U.S.--the Florida Keys Labor Day Storm of 1935 (892 mb) and Hurricane Camille of 1969 (909 mb). Katrina had the lowest pressure ever measured for a Category 3 hurricane; the previous record was 930 mb for Hurricane Floyd of 1999. Katrina's unusually low winds were primarily due to the fact that Katrina was a huge storm--the change of pressure from outside the storm to inside the storm happened over a large distance. It's the pressure gradient--the change of pressure with distance--that drives winds, not the pressure itself.

Death Toll
The official death toll so far is 1336, with 1090 of those victims in Louisiana and 228 in Mississippi. This makes Katrina at least the fifth deadliest U.S. hurricane of all time. The death toll could go much higher, making Katrina the third deadliest. Over 4,000 people are still listed as missing. Most of these missing people are probably alive and well, according to Kym Pasqualini, CEO of National Center for Missing Adults. However, she indicates that 1,300 of the missing from the most heavily damaged areas of New Orleans are a matter of great concern, and many of these people may have died in the storm.

The report quotes a preliminary figure of $75 billion in damage for Katrina, a number used by the American Insurance Services Group (AISG). This would make Katrina, by a least a factor of two, the costliest hurricane ever. A recent estimate by the world's largest re-insurance company, the Swiss Munich Re Foundation, put Katrina's total damage closer to $125 billion.

Forecast accuracy
NHC gives themselves high marks for forecast accuracy for the 2 1/2 days prior to Katrina's landfall. Indeed, their landfall location forecasts had errors more than a factor of two better than average. These exceptionally accurate forecasts likely saved hundreds of lives. On the other hand, NHC intensity forecasts for Katrina were up to a factor of two worse than average, and perhaps more lives could have been saved had these intensity forecasts been better.

Jeff Masters

Global warming and hurricanes part 1: The natural cycle

By: JeffMasters, 7:39 PM GMT on December 19, 2005

Before we can discuss the possible influence of global warming on hurricanes, we need to set the stage by talking about this natural cycle of hurricane activity we hear so much about. The Atlantic Multidecadal Oscillation (AMO) is a cyclic variation in the large-scale atmospheric flow and ocean currents in the North Atlantic Ocean that combine to alternately increase and decrease Atlantic sea surface temperatures (SSTs). As its name indicates, the AMO is "multidecadal"--meaning it operates on a time scale of multiple decades. The cool and warm phases last for 25-45 years at a time, with a difference of about 1�F (0.6�C) between extremes. These changes are natural. Analysis of tree rings, fossil coral, and sediments has shown that the AMO has been around at least 300 years, and probably much longer.

What has the AMO done in recent years?
As seen in Figure 1, the AMO has been though about two complete cycles since detailed measurements of the Atlantic began in the mid-1800s. A cool phase lasted 25 years from 1901-1925, a 44-year long warm phase from 1926-1969, and a 25-year long cool phase from 1970-1994. A new warm phase began in 1995, and the AMO index values since 2001 have been the highest on record. This has resulted in sea surface temperatures over the prime hurricane breeding grounds of the tropical North Atlantic being the highest on record, as well. The AMO index in 2004 was about the same as in 2003, but 2005 has seen about a 10% drop from 2004's level.

Figure 1. The AMO index, 1871 to 2003. The index was computed by averaging sea surface temperatures north of the Equator over the Atlantic Ocean, between 75�W and 7.5�W and south of 60�N. The red regions show warmer than average SSTs over the North Atlantic, and the blue regions, cooler than average. The "trend" has been removed, so the mean and long-term increase in SSTs are not visible. Image credit: Rowan, T.S., and Daniel Hodson, "Atlantic Ocean Forcing of North American and European Summer Climate", Science 309, 115-118, 2005. Reprinted with permission from SCIENCE, � 2005 AAAS. Permission from AAAS is required for all other uses.

How do hurricanes vary during warm and cool AMO cycles?
The AMO is thought to strongly influence the incidence of intense hurricanes, which more than double during the years when the warm phase of the AMO. For example, an average of 1.5 intense (category 3, 4, and 5) hurricanes per year formed in the Atlantic during the last cool phase of the AMO, 1970-1994, while 4.1 intense hurricanes/year formed during the current warm phase (1995 - 2005). The number of tropical storms and weak hurricanes do not change much between cool and warm AMO periods.

What causes the AMO, and can we predict it?
The causes of the AMO are not well-understood, but some "coupled" computer models that simulate the behavior of both the atmosphere and the ocean are beginning to shed light on this. One of the leading theories is that changes in the ocean's salt content causes a speed up or slow down of the Gulf Stream, due to the fact that density differences between lighter fresh water and heavier salty water drive weaker and stronger ocean currents, respectively. This circulation (called the "thermohaline circulation") is thought to cause the warm phase of the AMO and warmer Atlantic SSTs when it speeds up, and cooler SSTs and a cool AMO phase when it slows down. It is also possible, but less likely, that changes in atmospheric circulation cause the AMO. We are a long way from being able to predict when a particular phase of the AMO will begin or end. The last warm phase lasted for 44 years. The current cycle began in 1995, so it may not be until 2040 that the current active period of hurricane activity dies down.

What influence does global warming have on the AMO?
Since the instrument record extends back for only two cycles of the AMO, it is difficult to say if the record warmth in the current AMO cycle is unusual. It has been observed that the tropical North Atlantic SSTs have warmed approximately 0.3�C over the past 100 years due to global warming. However, the current thinking of climate experts is that global warming should act to dump increased fresh water into the North Atlantic and reduce the speed of the Atlantic thermohaline circulation. This would lead to a decrease in Atlantic SSTs, and a reduction of intense hurricanes. Either global warming hasn't acted to dump enough fresh water into the North Atlantic to affect the thermohaline circulation, or else the theory is wrong!

Jeff Masters

Climate Change

Tornado intercept vehicles

By: JeffMasters, 5:24 PM GMT on December 16, 2005

This Sunday, December 18, at 8pm, National Geographic is showing Tornado Intercept. This show highlights the use of the Tornado Intercept Vehicle (TIV), an armored monstrosity designed to be driven into the core of a weak (F-0 through F-1) tornado to collect scientific data, and film it with an IMAX movie camera. The TIV is really a modified 1997 Ford F-450 diesel pickup, engineered by IMAX cinematographers Sean Casey and Greg Eliason. The armor plating, 1/2" thick Lexan windows and other gizmos bring the weight of the vehicle up to 14,000 pounds, but it can still do 90 mph as it speeds off in pursuit of tornadoes. The TIV is equipped with a hydraulic system that lowers the vehicle flush with the ground, minimizing the risk of being overturned as a tornado's winds tear at the vehicle. The team is hoping to release an IMAX movie on tornadoes in 2008.

Figure 1. Sean Casey's "Tornado Intercept Vehicle" (TIV). Image courtesy of George Kourounis of

From what I gather, Sunday's show will not actually show a tornado penetration, and things did not always go smoothly during the chase season of 2005. A chaser journal from their 2005 storm chases reported:

The hood to our TIV (Tornado Intercept Vehicle) slammed into our windshield and then went airborne, that we have now reached our all time low. It's a bit humbling to walk a hundred yards down a highway to pick up pieces of the car you are driving. I tried not to make eye contact with cars as they drove by. We wire the hood back to the car and head toward a storm, not knowing that someone has siphoned our rear tank empty of diesel fuel. (The truck is making a sound like a cross between that of a rattlesnake and a cicada beetle. I'm sensitive to all sounds, smells and vibrations that the vehicle makes since we've had nine breakdowns, including two car fires.)

The Tornado Attack Vehicle
There is another tornado intercept vehicle out there you may have read about, called the TA-1 or Tornado Attack Vehicle. The TA-1 was built by Steve Green, a race car driver from Mooresville, N.C. The TA-1 is a modified Baja trophy truck with armor plating, heavy-duty roll bar, and Lexan bullet-proof windows. It is designed to withstand 240 mph winds, according to Green. The TA-1 made news last year when Green put up a ride into a tornado up for sale on Ebay. Thirteen people bid on the auction, and the top bidder paid $145,000 for the opportunity to be driven into the heart of a tornado. The Tornado Attack web site says they intercepted three tornadoes in 2005, but none of the video footage shows them actually penetrating a tornado, and I don't think this has happened yet.

So, it hasn't happened yet, but the day is soon coming when one of these vehicles will drive into a tornado. I'm sure there will be another majorly hyped television show when it happens, assuming the people doing this don't get killed.

Figure 2. Steve Green's TA-1 "Tornado Attack Vehicle".

Coming Monday and all next week: In depth discussions of the hurricane/global warming connection. I would liked to have posted this discussion during the height of hurricane season, but it has taken a long time to do the research on this needed to really understand what is going on!

Jeff Masters

P.S., just for laughs: Check out what one creative Photoshop user has done to the Tornado Intercept Vehicle, making it into a Chicken Intercept Vehicle.


The coldest clouds

By: JeffMasters, 5:21 PM GMT on December 15, 2005

In the wunderphoto posted by carlskou today (see image below), the caption reads: What's that? Well, I'll answer that question!

That is a Polar Stratospheric Cloud (PSC), also known as a nacreous or mother-of-pearl cloud. These clouds of ice crystals form in the very coldest reaches of the stratosphere over both poles in winter, at an altitude of 25-30 km. These ice-crystal clouds are frequently iridescent, meaning that they diffract the suns's light and form brilliant spots or borders of colors, usually red and green, up to about 30� from the sun.

Polar Stratospheric clouds are fairly rare, because they require extremely cold temperatures that are not often found in the atmosphere. However, residents of Norway, Sweden, Finland, Alaska, northern Canada, and other polar locations can expect to see a lot more of these in the future. Why? Because the stratospere is cooling. The Arctic stratosphere has cooled 3�C in the past 20 years due the combined effects of ozone loss, greenhouse gas accumulation, and natural variability. Winter 2005 temperatures in the Arctic stratosphere were the coldest ever recorded. A large part of this cooling is due to the greenhouse effect. Yes, the surface and lower atmosphere are warmed by the greenhouse effect, but this means that the atmosphere must cool somewhere else to compensate. Much of this cooling happens in the stratosphere. This can best be understood by considering that the Earth is in "radiative equilibrium"--the amount of solar energy coming in is balanced by the amount of energy going out. Surface warming must be balanced by upper-atmosphere cooling, since the amount of solar radiation the Earth receives does not change, and satellite measurements have shown that the amount of heat going out to space from the Earth has not changed, either.

What does all this stratosperic cooling mean for the climate? That is mostly unknown. We do know that PSCs act to greatly accelerate stratosperic ozone destruction, since the chemical reactions that destroy ozone happen much faster on the reactive surfaces that PSCs provide. A recent model study (Rex et. al., 2004), indicates that future Arctic ozone depletion could be much worse than expected, and that each degree Centigrade cooling of the Arctic may result in a 4% decrease in ozone. This ozone loss will occur despite the fact that concentrations of ozone-destroying chlorofluorocarbons (CFCs) are no longer rising, thanks to the international agreements that have phased out CFC use. It's a very good thing that the nations of the world acted quickly and effectively to ban CFC use when they did, or else we would have likely seen an Arctic ozone hole open up each Spring to complement the Antarctic ozone hole.

Tomorrow's topic: Penetrating tornadoes with modified vehicles.

Jeff Masters

Atmospheric Phenomena

Air pollution episode over western U.S.

By: JeffMasters, 2:19 PM GMT on December 14, 2005

Particle pollution in the western U.S. has reached Unhealthy for Sensitive Groups and Unhealthy levels on the U.S. EPA's Air Quality Index (AQI) due to a stagnant weather pattern impacting the region. Some regions of California have reported unhealthful levels of particle pollution ten straight days; on Tuesday, Bakersfield, Fresno, and Sacramento all reported Unhealthy AQI levels. The unhealthful conditions are expected to continue today, and Bakersfield, Fresno, Hanford, and Visalia, in California, and Phoenix, Arizona have all declared air quality Action Days.

Figure 1. Winds over the western U.S. have been light the past ten days, generally less than 10 mph.

Figure 2. Visibility has been reduced below seven miles in many regions of Califonia due to air pollution and fog today.

The jet stream has been locked in place the past two weeks with a ridge of high pressure over the western U.S., and a trough of low pressure over the eastern part of the country. This pattern has steered cold air and storms into the eastern U.S., but left the western U.S. under high pressure with light winds and no rain. With no wind to flush the stagnant air out, and no rain to deposit the pollutants to the ground, particles of air pollution have built up to unhealthful levels. This weather pattern is expected to continue for at least another week. Beginning December 22 or 23, long range computer models are showing a major shift in the jet stream pattern, which may allow rain and wind to return once more to the western U.S.--and bring the eastern U.S. out of its deep freeze.

Check your local air quality forecasts and conditions by visiting the EPA AIRNow website at and selecting Local Forecasts and Conditions. If you are under an air pollution action advisory, limit prolonged or heavy exertion, reduce your activity time or substitute another activity that involves less exertion. Plan outdoor activities for days on which particle levels are lower. Reduce particle levels in the atmosphere by reducing your use of electricity and other particle sources such as automobiles, wood-burning stoves, and fireplaces.

Jeff Masters

Air and Water Pollution

No Zeta: Hurricane Season is over

By: JeffMasters, 2:37 PM GMT on December 13, 2005

The strong extratropical low pressure system southwest of the Azores Islands is showing no signs of tropical development today. The amount of deep convection near the low's center has decreased since yesterday, and with wind shear values of 20 knots overhead and steadily increasing, this storm has no chance to develop into Tropical Storm Zeta. The low will get absorbed into an approaching cold front on Wednesday and rapidly dissipate.

Elsewhere in the tropical Atlantic, wind shear levels are very high and expected to remain high for at least the next week, making tropical storm formation very unlikely. Long range models show a weak extratropical low developing near the Canary Islands late in the week, but wind shear is expected to be too strong to allow this low to develop into a tropical storm. I can now confidently predict that the end of the Hurricane Season of 2005 has arrived! Look for my next update on the tropics at the beginning of next year's hurricane season, on June 1. My blog until then will primarily focus on climate change, reviewing the Hurricane Season of 2005, and other topics of interest.

Figure 1. Map of all coastal areas subjected to hurricanes warnings (red) and tropical storm warnings (yellow) during the Hurricane Season of 2005.

Jeff Masters

Why no hurricanes for Puerto Rico this year?

By: JeffMasters, 3:06 PM GMT on December 12, 2005

A brief update on the tropics today:

A strong extratropical low pressure system (993 mb) is just south of the Azores Islands today, in the far eastern Atlantic. This storm is generating winds of 40-45 mph, and has the potential to make the transition to a tropical storm later in the week as it moves slowly westward. Water temperatures beneath it are 21-22C and wind shear is a low 5-10 knots. However, strong wind shear associated with an appraoching trough is expected to impact the storm on Wednesday, which may not leave it enough time to make the transition to Tropical Storm Zeta.

Why no hurricanes for Puerto Rico this year?

I've plotted an image (Figure 1) showing every stretch of Atlantic coast placed under a hurricane or tropical storm warning during the Hurricane Season of 2005. The phenomenal number of landfalling storms in 2005 led to warnings being hoisted for the entire Atlantic coast from Plymouth Massachusetts southwards to Costa Rica. A small section of Guatemala and Honduras escaped warnings, but nonetheless received damage from heavy rains from at least one tropical storm. Most of the Caribbean islands also suffered blows from at least one hurricane, with the notable exception of the area around Puerto Rico--the northeastern Caribbean
--where no storms occurred. Why did this region escape the wrath of the Hurricane Season of 2005?

Figure 1. Map of all coastal areas subjected to hurricanes warnings (red) and tropical storm warnings (yellow) during the Hurricane Season of 2005.

One obvious possibility is that wind shear levels in the northeast Caribbean happened to be higher than average. This is the theory advanced by Dr. Bill Gray of Colorado State University in his summary of the 2005 hurricane season. However, when one plots the average wind shear over the various portions of the Atlantic for 2005 (Figure 2), only the western Caribbean shows near average levels of wind shear. The ocean areas on either side of Puerto Rico--the eastern Caribbean and the tropical Atlantic--both show below-average levels of wind shear.

Figure 2. Historical average wind shear levels (black lines) and observed wind shear for the 2005 hurricane season (blue lines). The Gulf of Mexico, eastern Caribbean, and tropical Atlantic all had wind shear levels well below average for much of the 2005 hurricane season.

Another possibility is that large amounts of African dust inhibited tropical storm formation in the northeast Caribbean. This is likely a significant factor, since many large clouds of African dust tended to push across the Atlantic and into the northeast Caribbean between late July and early September of 2005, the prime part of hurricane season for this region. I can recall in particular that the dry air associated with Tropical Depression Ten helped kill this storm as it approached the northeast Caribbean in mid-August. Unfortunately, the dry air diluted enough by the time it reached the Bahamas that Hurricane Katrina was able to form from the remnants of Tropical Depression Ten.

Figure 2. Visible satellite image of one of the many clouds of African dust that crossed the Atlantic during the Summer of 2005.

Jeff Masters

The tropics are finally quiet

By: JeffMasters, 7:32 PM GMT on December 09, 2005

There is no tropical storm activity in the Atlantic today for the first time since early November. The remains of Hurricane Epsilon are just a swirl of low clouds at the base of a cold front sweeping towards Europe, and are not a threat to regenerate into a tropical storm. However, all of the computer models are forecasting that a strong extratropical low pressure system will develop on Sunday near the region Epsilon died, and this new low has the potential to develop into Tropical Storm Zeta by late next week as it moves slowly westward over the mid-Atlantic. This storm will not be a threat to any land areas, and is expected to recurve harmlessly to the northeast later in the week.

Blog topics for the remainder of the year
I am working on a number of blog topics related to hurricane season that I hope to post over the next two weeks. There include:

1) Why did Puerto Rico and the northern Leeward Islands get missed this year?

2) What was the global hurricane season like? Did the other oceans experience as many intense hurricanes as the Atlantic, supporting a global warming connection?

3) Why was Katrina's storm surge so huge?

4) Was this year's incredible hurricane season partially attributable to global warming?

My next update will be on Monday.

Jeff Masters

Last day of hurricane season?

By: JeffMasters, 2:08 PM GMT on December 08, 2005

Epsilon is finally dying. Fifty knots of wind shear have ripped away Epsilon's deep convection, and Epsilon is now just a swirl of low clouds. Today will be the final day of Epsilon's life, and likely the final day of the Hurricane Season of 2005. There is still a possibility that an extratropical low expected to form from Epsilon's remnants and drift slowly westward may be able to generate into Tropical Storm Zeta by the middle of next week, but I give this only a 30% chance of happening. Water temperatures are a cool 22-23C in the region. While both Delta and Epsilon did form from similar extratropical lows in the same region, the computer models are predicting that the new storm will have a more limited amount of time to develop (four days) before it gets recurved northeastward by a trough of low pressure. This probably is not enough time for it to make the transition to a tropical storm.

Jeff Masters

Epsilon sets new records

By: JeffMasters, 3:52 PM GMT on December 07, 2005

Epsilon has now remained a hurricane for five days, making it the longest lived December hurricane on record. The previous record was just over four days, set by an unnamed 1887 hurricane. Epsilon has been a hurricane long enough to push the Hurricane Season of 2005 into sixth place for the most number of days a hurricane has been present--50.25 days. The record is 1893, with 72 days. If Epsilon can hang around until the 4 pm advisory on Friday, 2005 will tie 1995 for the second highest number of days with a named storm in the Atlantic, 120.5. The record is 136 named storm days in 1933. Not bad for a storm that was expected to be a remnant low four days ago, according to the first NHC forecast predicting its demise!

Epsilon is not done with us yet--the satellite presentation looks excellent, and there is still no sign that the strong westerly winds associated with a trough just to the cyclone's west are beginning to shear the storm apart. This is expected to happen on Thursday and Friday, but we've heard that before! The current best guess is that Epsilon will be destroyed by wind shear from the trough by Saturday. However, several models are indicating that Epsilon may reform into an extratropical low pressure system west of the Azores Islands early next week, then drift southwestward and gradually acquire tropical characteristics, potentially becoming a tropical storm again. There is also a slight chance a tropical storm could form in the ocean waters just north of Panama next week. Overall, I estimate that there is a 30% chance we'll be watching an Atlantic tropical storm at this time next week, either Epsilon or Zeta.

Jeff Masters

Another tough hurricane season in 2006

By: JeffMasters, 3:25 PM GMT on December 06, 2005

Get ready for another tough hurricane season in 2006. If the forecast team at Colorado State University (CSU) founded by Dr. Bill Gray (now headed by Dr. Phil Klotzbach) is correct, we are in for another much more active than usual hurricane season, with 17 named storms and 9 hurricanes. The average Atlantic season has only 11 named storms and 6 hurricanes. In their forecast for the upcoming hurricane season released today, the CSU team also projects that the U.S. will be at high risk from strikes by intense hurricanes again, with an 81% chance of a strike by a Category 3, 4, or 5 hurricane. However, the forecast notes that the from a purely statistical point of view, the number of landfalling hurricanes and major hurricanes in the U.S. should decrease in 2006 from what we have seen during 2005 and 2004. They note:

It is rare to have two consecutive years with such a strong simultaneous combination of high amounts of major hurricane activity together with especially favorable steering flow currents. The historical records and the laws of statistics indicate that the probability of seeing another two consecutive hurricane season like 2004-2005 is very low. Even though we expect to see the current active period of Atlantic major hurricane activity to continue for another 15-20 years, it is statistically unlikely that the coming 2006 and 2007 hurricane seasons, or the seasons which follow, will have the number of major hurricane US landfall events as we have seen in 2004-2005.

The CSU team uses observations of monthly average atmospheric winds and pressures over six specific regions of the globe taken this Fall to determine whether favorable or unfavorable conditions will exist for the 2006 hurricane season. All six of these "predictors" are favorable for an active 2006 hurricane season. A condensed summary:

1) El Nio, which acts to suppress Atlantic hurricane activity, is not expected to be active during the 2006 hurricane season. It is more likely that neutral or even La Nia conditions will develop, which are favorable for Atlantic hurricane activity.

2) The stratospheric quasi-biennial oscillation (QBO), an oscillation in the stratosphere that creates alternating westerly and easterly winds there, is expected to be in it west phase during the hurricane season of 2006. The west phase of the QBO has been shown to provide favorable conditions for development of tropical cyclones in the deep tropics.

3) The observed pressure and wind patterns over the North Atlantic will allow stronger than normal southerly winds to keep sea surface temperatures over the entire North Atlantic well above normal during 2006. Sea surface temperatures during 2005 were the highest measured since at least 1950, and helped fuel 2005's record-breaking intense hurricanes. Sea surface temperatures during the 2006 hurricane season may be just as warm.

4) Perhaps most importantly, observed wind and pressure patterns this Fall indicate that upper-level winds in the upper atmosphere (200 mb) will blow from the east during the hurricane season of 2006, like they did during 2005. This results in low wind shear over hurricane formation regions of the tropical Atlantic. Low wind shear is the key ingredient needed for tropical storm formation and intensification.

How good are these long-range hurricane forecasts issued in December? Last year, the December forecast called for an average 2005 hurricane season with 11 named storms, six of them becoming hurricanes. Obviously, the forecast was a bust--we had 26 named storms and 14 hurricanes. The updated forecast issued on May 31 of 2005 performed much better--15 named storms were forecast, with eight hurricanes. However, over the past five years (not including the forecast for the 2005 season), the skill of the December hurricane forecasts by the CSU team has been quite good--in four out of five years, the predicted number of named storms was within three of the actual number. Tune in April 4, when the CSU team issues their updated forecast for the 2006 hurricane season. Maybe Hurricane Epsilon will be gone by then!

I'll talk more about Epsilon tomorrow.

Jeff Masters

Why so many U.S. hurricanes the past two years?

By: JeffMasters, 4:51 PM GMT on December 05, 2005

Before I answer the title question, let's talk about Epsilon. This hurricane refuses to die, despite cold waters and high wind shear. The latest model projections continue to keep it as a hurricane for at least two more days, which would make 2005 break the record for most number of hurricane days (50, set in 1995) and most number of days with a named tropical storm (120.5, set in 1995). Beyond three days from now, I really don't see how the storm can survive, since wind shear levels will increase to more than 50 knots, which will surely tear the storm apart. Nothing else is brewing in the tropics, although there is a marginal possibility of something developing north of Panama a week or so from now.

Why have so many hurricanes hit the U.S. in 2004 and 2005?
The 1995 - 2003 hurricane seasons were quite active, but only 3 of 32 (9%) major hurricanes that formed in the Atlantic made landfall in the United States, much below the climatological average of 30% for the entire 20th century. This lack of hurricane strikes occurred because a trough of low pressure was frequently located over the East Coast during these years, and the flow of winds through the trough tended to recurve hurricanes northeastward out to sea before they could strike land. However, in 2004 and again in 2005, this trough was mostly absent, and an unusually strong ridge of high pressure was in place which tended to steer hurricanes into the U.S. and not allow recurvature. Seven of 13 (54%) major hurricanes that formed in the Atlantic made United States landfall as major hurricanes during 2004 and 2005.

So, what caused this unusually strong ridge of high pressure to develop over the eastern U.S.? According to Dr. Bill Gray's hurricane forecast team at Colorado State University, this ridge formed in response to a strong warming of the ocean in the central North Pacific. Figure 3 shows the difference in Pacific sea surface temperatures during August-October 2004-2005 from August-October 1995-2003. Central North Pacific sea surface temperatures were up to 1.3C (2.3F) warmer in 2004-2005 compared to 1995-2003, leading to a deflection of the jet stream dowstream of the warm pool. The jet stream assumed a standing wave pattern, resulting in a ridge of high pressure over the central Pacific, trough of low pressure over the western U.S., and high of high pressure over the eastern U.S. It was this ridge of high pressure over the eastern U.S. that steered so many storms into the country during 2004-2005. Why did the ocean warm in the central North Pacific, and will that warm pool remain in place for the 2006 hurricane season? That is unknown.

Tune in tomorrow, when Dr. Bill Gray's forecast team releases their 2006 hurricane season forecast.

Figure 3. August-October 2004-2005 sea surface temperatures minus August-October 1995-2003 sea surface temperatures. Note the large warming of 1.3 degrees C in the central North Pacific. Image credit: Dr. Bill Gray's hurricane forecast team at Colorado State University.

Jeff Masters

Epsilon refuses to obey the rules

By: JeffMasters, 7:45 PM GMT on December 04, 2005

Epsilon refuses to obey the rules. Not only has Epsilon refused to die as expected--it has strengthened in the past day to near Category 2 strength. Epsilon is traversing 22-23C waters, which are a full four degrees C (7 F) below what is normally thought of as the minimum needed to allow a hurricane to strengthen. The upper level winds are unfavorable--Epsilon was been under 20 knots of shear the past two days. It is unusual to see a hurricane intensify in the face of 20 knots of shear (although Wilma managed to do so). It is unheard of for a hurricane to intensify in the face of 20 knots of shear, and with 22C water temperatures under it. Like I've been saying about this entire Hurricane Season of 2005, the normal rules do not apply. Epsilon is another storm that we do not understand, and I hope someone out there in grad school is taking data on this storm and writing a Ph.D. thesis on it!

Epsilon will continue to hang around most of the week. A strong ridge of high pressure has built over it, forcing it on a eastward track that will keep it from passing over really cold 20C waters to the northeast that would have surely killed it. By Wednesday, this ridge of high pressure is expected to force Epsilon southward and then southwestward towards warmer waters. However, by this point, the shear over Epsilon should be somewhere near 40 knots, which should be able to rip the storm apart. This should put a end once and for all to the Hurricane Season of 2005. I don't expect anything else to develop this month, since forecast wind shear levels over the Caribbean Sea the next ten days are now looking only marginally favorable for tropical storm formation.

Jeff Masters

Epsilon a hurricane!

By: JeffMasters, 3:56 PM GMT on December 02, 2005

Epsilon has been upgraded to a 75-mph hurricane, only the 6th December hurricane ever recorded. Epsilon joins the ranks of Hurricane Nichole (1998), Hurricane Lili (1984), Hurricane Alice (1954), an unnamed 1925 storm, and an unnamed hurricane from 1887 as the only December hurricanes recorded in the Atlantic. Epsilon's location is the second farthest north and east of any December hurricane (next to Nicole of 1998), and marks the record 14th hurricane to form in the Atlantic this year. The previous record was 12 hurricanes, set in 1969.

Epsilon is apparently traversing a very narrow ribbon of relatively warm ocean waters of 75 - 77 F (22-23C), which has allowed its intensification. Water temperatures across the entire North Atlantic are still unusually high, averaging about 2 F higher than normal. Very cool waters of about 70 F (21 C) lie just 200 miles from Epsilon, so its intensification to hurricane status is likely short-lived. By Saturday night, cold waters and increasing wind shear should put an end to Epsilon's life--and perhaps the Hurricane Season of 2005.

Long range computer models are forecasting somewhat favorable conditions for tropical storm formation to return next week to the Caribbean Sea, and last through mid-December. I expect there is at least a 40% chance that Tropical Storm Zeta will appear in the Caribbean by the middle of the month.

I'll delay my summary of why the United States suffered so many hurricane strikes the past two years until next week.

Figure 1. Hurricane Epsilon (987 mb, 75 mph winds) at 9:45 am EST December 2, 2005.

Jeff Masters

The unbelievable Hurricane Season of 2005

By: JeffMasters, 2:41 PM GMT on December 01, 2005

It is finally December, and hurricane season is officially over. But this is the Hurricane Season of 2005. The normal rules do not apply. True to its character all year, the Hurricane Season of 2005 continues to defy the normal rules. Tropical Storm Epsilon is still out there in the mid-Atlantic, and is expected to be with us another two days before increasing winds shear and cold waters weaken it and convert it to a regular extra-tropical low. The Azores Islands need to be concerned about this storm, but Epsilon is not a threat to any other land areas. Perhaps the last casualty has been inflicted, the last damage done by the Hurricane Season of 2005.

How can one summarize this unbelievable hurricane season? I strongly believe that this was a once-in-a-lifetime hurricane season. To have 26 named storms, 13 hurricanes, and three of the six strongest hurricanes of all time in one year so greatly exceeds our meteorological understanding of what is possible, that I believe that was a once in 500 years kind of season. Let us consider some of the major records that were broken in 2005:

Seasonal records set in 2005

- Most tropical storms: 27. Old record: 21 in 1933.

- Most hurricanes: 14. Old record: 12 in 1969.

- Most Category 5 hurricanes: 3 (Katrina, Rita, Wilma. Emily may be classified as a Category 5 upon re-analysis.) Old record: 2 in 1960 and 1961.

- Most hurricane names to be retired: 6 (Dennis, Emily, Katrina, Rita, Stan, Wilma, and possibly others). Previous record: 4 in 1955, 1995, and 2004.

- Most major hurricanes: 7 (Dennis, Emily, Katrina, Maria, Rita, Wilma, Beta). Ties record of 7 set in 1950.

- Most major hurricanes to hit the U.S.: 4 (Dennis, Katrina, Rita, Wilma). Previous record: 3 in 1893, 1909, 1933, and 1954.

- Most damage ever recorded in a hurricane season: $150 billion. Previous record: approximately $50 billion dollars (normalized to 2005 dollars) set in 1992 and 2004.

-Highest Accumulated Cyclone Energy (ACE) index: 245. Previous record: 243 (1950). Average for a season is 93.

-Latest end to a hurricane season: January 6 Previous record: January 5, for the 1954-55 hurricane season.

Notable near records for the season

- Second highest number of tropical storms to hit U.S.: 7 (The record was 8 in 1916 and 2004). Note that Hurricane Ophelia is not considered a U.S. strike, although it did bring hurricane conditions to the North Carolina coast.

- Second highest number of hurricanes to kill 1000+ people: 2 (Katrina and Stan). All time record: 3 (1780).

- Second highest number of named storm days: 126.5. All time record: 136 (1933).

Single storm records:

- Strongest Atlantic hurricane ever: Wilma, 882 mb central pressure. Old record: Hurricane Gilbert (1988), 888 mb.

- Fastest intensification ever by an Atlantic hurricane: Wilma. Wilma's pressure dropped from 982 millibars to 882 millibars in 24 hours on Oct 19, a rate of 4.2 millibars an hour. Previous record: Gilbert (1988) dropped 3 mb/hour over 24 hours. Wilma's pressure fell 9.7 mb/hour over six hours early on Oct. 19, beating Hurricane Beulah's drop of 6.3 mb/hour in six hours in 1967.

- Most damaging hurricane ever: Katrina, $100 billion plus. Old record: Hurricane Andrew (1992), $50 billion in 2005 dollars.

- Greatest storm surge from an Atlantic hurricane: Katrina, 28-30 feet. Old record: Hurricane Camille (1969), 24.6 feet.

- Dennis became the most intense hurricane on record before August when a central pressure of 930 mb was recorded.

- Emily eclipsed the record previously set by Dennis for lowest pressure recorded for a hurricane before August when its central pressure reached 929 mb.

- Vince was the furthest north and east that a storm has ever developed in the Atlantic basin.

- Vince was the first tropical cyclone in recorded history to strike the Iberian Peninsula.

- Delta was the first tropical cyclone in recorded history to strike the Canary Islands.

Monthly records


- Two named storms formed (Arlene and Bret). Only 1957, 1959, 1968, and 1986 had two or more named storms form during the month of June.


- Five named storms formed (Cindy, Dennis, Emily, Franklin, and Gert). This is the most on record for July.

- Two major hurricanes formed (Dennis and Emily). This is the most on record.

- 25.25 named storm days occurred. This is the most on record.

- 10.75 hurricane days occurred. This is the most on record.

- 5.75 intense hurricane days occurred. This is the most on record.


- Five named storms formed (Harvey, Irene, Jose, Katrina and Lee). Only 1990, 1995 and 2004 had more than five named storms form during the month of August.


- Five hurricanes formed (Maria, Nate, Ophelia, Philippe and Rita). This ties 1955, 1969, 1981, 1998 and 2000 for the most hurricanes to form during the month of September.


- Six named storms formed (Stan, Tammy, Vince, Wilma, Alpha and Beta). This ties 1950 for the most named storm formations during the month of October.

- Four hurricanes formed (Stan, Vince, Wilma and Beta). Only 1950 had more hurricanes develop during the month of October.

- Two major hurricanes formed (Wilma and Beta). This ties 1950, 1961, 1964 and 1995 for the most intense hurricanes to form during the month of October.

- Five intense hurricane days occurred. Only 1954 and 1961 recorded more intense hurricane days.


- Three tropical storms formed in November (Gamma, Delta, and Epsilon). This breaks the record of two storms set in six years, most recently in 2001.


- Epsilon was a hurricane for 5.25 days, making it the longest lived December hurricane on record. The previous record was just over four days, set by an unnamed 1887 hurricane.


- Tropical Storm Zeta was the longest-lived January storm on record (six days). January 2006 had the greatest number of named storm days ever recorded in January (six).

Earliest Storm Formation records
- Earliest formation of a season's 4th Storm
- Earliest formation of a season's 5th Storm
- Earliest formation of a season's 6th Storm
- Earliest formation of a season's 7th Storm
- Earliest formation of a season's 8th Storm
- Earliest formation of a season's 9th Storm
- Earliest formation of a season's 10th Storm
- Earliest formation of a season's 11th Storm
- Earliest formation of a season's 13th Storm
- Earliest formation of a season's 14th Storm
- Earliest formation of a season's 15th Storm
- Earliest formation of a season's 16th Storm
- Earliest formation of a season's 17th Storm
- Earliest formation of a season's 19th Storm
- Earliest formation of a season's 20th Storm
- Earliest formation of a season's 21st Storm
- Earliest formation of a season's 22nd Storm
- Earliest formation of a season's 23rd Storm
- Earliest formation of a season's 24th Storm
- Earliest formation of a season's 25th Storm
- Earliest formation of a season's 26th Storm

I credit Dr. Bill Gray's Hurricane Season of 2005 Verification posted on his web site for compiling many of these records, along with wunderblogger Cory Pesaturo. You will find many more records listed on their web pages.

Jeff Masters

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

Category 6™


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