Category 6™

95L fizzles; Sierras brace for 5-10 feet of snow

By: JeffMasters, 12:10 AM GMT on December 31, 2007

A non-tropical low pressure system dubbed Invest 95L, near 27N 38W, way out in the middle of the Atlantic Ocean, has gotten less organized since yesterday. The storm cut off from the jet stream and acquired some subtropical characteristics yesterday, as it sat nearly stationary over waters of 22-23° C. However, satellite imagery shows fewer heavy thunderstorms than yesterday, and the storm has a more extratropical appearance as it interacts with a cold front to its north.

This evening's QuikSCAT pass showed winds up to 50 mph on the west side of 95L. Wind shear is about 30 knots over 95L, and this shear is expected to be 20-40 knots for the next two days. This is probably too high to allow 95L to develop into a subtropical storm, and wind shear is forecast to grow stronger as the storm begins moving west-southwest on Tuesday. By Thursday, a trough of low pressure is expected to recurve 95L northeastward, and the storm is not expected to affect any land areas.

Huge blizzard expected in the California Sierras
One of the most severe blizzards of the past 50 years is expected to affect California's Sierra Mountains beginning Thursday night, January 3. A powerful low pressure system will establish itself off the coast of Oregon, and bring a series of heavy snow events with blizzard conditions to the Sierras through Monday. Five to ten feet of snow are possible in the high mountains. Travel will be nearly impossible in the high country next weekend, with white-out conditions and wind gusts near hurricane strength. This is going to be a great storm for filling the reservoirs that supply the northern half of the state with its water. Reservoirs should be at full capacity next summer, easing fears of a significant water shortage. Last winter's snows failed to fill the reservoirs to even 50% of capacity.


Figure 1. Estimated rainfall for December 30 for Georgia. Atlanta got one of its heaviest rains of the year today.

Happy New Year! I'll be back January 2 to talk about the Georgia drought. Heavy rains that fell today may have been just enough to keep Atlanta from setting a record for its driest year since record keeping began in 1930.

Jeff Masters

Winter Weather

One more named storm for '07?

By: JeffMasters, 5:38 PM GMT on December 29, 2007

OK, here we go one more time in '07! A non-tropical low pressure system dubbed Invest 95L, near 27N 38W, way out in the middle of the Atlantic Ocean, has cut off from the jet stream and is beginning to acquire tropical characteristics as it sits nearly stationary over waters of 22-23° C. Satellite imagery shows a curved band of heavy thunderstorms arcing 3/4 of the way around the large center of circulation. This morning's QuikSCAT pass showed winds of 30-35 mph in this band. Wind shear is about 20 knots over 95L, and this shear is expected to be 20-30 knots for the next two days, which may be low enough to allow the storm to develop into a subtropical storm before the year is out. The storm would be called Subtropical Storm Pablo, since the strongest winds are well removed from the center, and the system does not have a fully warm core.


Figure 1. Visible satellite image of Invest 95L in the middle of the Atlantic Ocean.

The four reliable computer models all predict little movement of 95L for the remainder of 2007, then a track to the west-southwest towards Puerto Rico and the northern Lesser Antilles Islands beginning on New Year's Day. Wind shear is forecast to rise to prohibitively high levels by January 1, so it is highly unlikely this storm will survive to affect any land areas.

I'll have an update by Sunday evening if this storm hangs together.

Jeff Masters

Treating scientists as bags of mostly water

By: JeffMasters, 4:01 PM GMT on December 26, 2007

During the holiday season, it's natural to ask philosophical questions such as, "what is the essence of being human?" Well, one way to answer that question is purely scientifically. Humans are mostly water (ugly bags of mostly water, according to Microbrain, Stardate 41463.9, Star Trek: The Next Generation,, Episode 17). More than half the human body is made up of water, and we can use that fact to measure how many humans are present at large gatherings. Such an experiment was performed at the 2006 American Geophysical Union (AGU) meeting in San Francisco, as reported in a November 2007 paper by Darin Desilets et al. of the University of Arizona. The experiment made use of the fact that cosmic rays are continually bombarding the earth, creating fast neutrons as a by-product of nuclear disintegrations. When these neutrons encounter large concentrations of hydrogen (such as found in ugly bags of mostly water), they get scattered. One can look at the resulting scattering pattern and deduce how much hydrogen is present, and make an estimation of the number of people present.


Figure 1. Ugly bag of mostly water (and co-founder of the Weather Underground) Perry Samson (right) poses in front of his Poster at the 2007 AGU meeting. Also pictured: Russ Rew and Mohan Ramamurthy of Unidata. Fast cosmic ray neutrons scattered from their bodies were used to help estimate the number of people present at the 2006 meeting.

The equipment needed to do so costs about $10,000, and was set up in the Moscone Convention Center in San Francisco during the 2006 AGU meeting. The scientists were able to show when lunch breaks occurred by pointing out a sharp reduction in neutron scattering when all the scientists filed out to grab a bite to eat. Desilets et al. estimated about 1,700 scientists were present in the Exhibit Hall of the convention center during the height of the conference, which is probably a reasonable estimate, given the stated capacity of 3575 people. The technique can also be used to perform measurements of water content of snow and soil, and Desilets et al. advertise that they are open to paid invitations to count crowds at Rio de Janerio's Carnival, Pamplona's running of the bulls, and the next World Cup Finals.

Happy New Year, everyone! I'll be back with a new blog on January 2.

Jeff Masters

References
Desliets, D., M. Zreda, T. Ferre, 2007, Scientist Water Equivalent Measured With Cosmic Rays at 2006 AGU Fall Meeting, EOS, TRANSACTIONS AMERICAN GEOPHYSICAL UNION, VOL. 88, NO. 48, PAGE 521, 2007.

Humor

Next century's most important place in the world--Greenland?

By: JeffMasters, 1:58 PM GMT on December 21, 2007

If one had to pick the region of the world most likely to influence the course of human history this century, the Middle East would be the obvious choice, due to its political volatility and rich oil resources. However, the Middle East may have a significant challenger next century from a seemingly unlikely place--Greenland. Why Greenland? Well, the Greenland ice sheet holds enough water to raise global sea level 7 meters (23 feet). There are worrisome signs that the ice sheet might be more vulnerable than we thought to significant melting near the end of the century, according to research results presented at last week's annual meeting of the American Geophysical Union (AGU) in San Francisco. The meeting is the world's largest annual gathering of climate change scientists.

For climate change scientists, Greenland is clearly the most important place in the world. You could tell this by the way glaciers with unpronounceable names like "Kangerdlugssuaq" rolled off their tongues in a smooth, practiced manner at talks given at the AGU meeting. At least 120 presentations focused on the Arctic or Greenland, and fully 52 of these concerned Greenland. I attended roughly 20 of these talks, and most of the presenters made it clear that they were quite concerned about the future of Arctic sea ice and the Greenland ice sheet, particularly in light of the astounding Arctic sea ice melt that occurred in 2007. A number of these talks raised the possibility that we've reached a tipping point in the Arctic. A complete loss of summertime sea ice may occur between 2013 and 2040, three of the presenters said, with the resulting warming dooming the Greenland ice sheet to a slow but inevitable melting process over a period of centuries. None of the presenters expressed the view that the current melting of the Greenland ice sheet and Arctic sea ice was due to a natural cycle that would completely halt or reverse in the next few years or decades.

At a talk on "The Recent Arctic Warm Period", Dr. Jim Overland, an Arctic expert with NOAA's Pacific Marine Environmental Laboratory, didn't offer his view on whether a tipping point had been reached. Instead, he asked the audience to vote. The options he presented:

* A The melt back of Arctic sea ice observed in 2007 is permanent and will not lessen.
* B Ice coverage will partially recover but continue to decrease.
* C The ice would recover to 1980s levels but then continue to decline over the coming century.

Both Options A and B had audience support, but only one brave soul voted for the most conservative option C.


Figure 1. A research submarine breaks through the Arctic ice. Image credit: Bernard Coakley.

The latest news from Greenland
I was amazed see the tremendous breadth and intensity of research efforts focused on Greenland and the Arctic, presented at AGU. Extra funding has been given to research efforts as part of the International Polar Year (IPY) program, scheduled to run March 2007 through 2009. Satellites like Icesat and GRACE measure the extent of Greenland's ice from above, aided by a fleet of small and large research aircraft. Scientists now have unmanned aircraft that can use runways or be launched by slingshot that can measure the extent of Greenland's melt water lakes. The air armada will be joined next year by the Total Pole Airship, the first blimp used for Arctic studies. Manned and unmanned submarines measure the thickness of the sea ice surrounding the island, and both permanent and temporary bases dotted across Greenland and the polar sea ice house scientists doing land-based studies. Ships and buoys also add data from the ocean areas.

A short list of the results presented at AGU all point to an ice sheet in peril:

- Melting of snow above 2000 meters elevation on Greenland reached a new record in 2007 (Tedesco, 2007).

- Leigh Stearns of the University of Maine's Climate Change Institute showed that the contribution of Greenland melting to global sea level rise has doubled in the last five years. According to the 2007 IPCC report (see Figure 4.18), Greenland may account for as much as 10% of the total global annual sea rise of about 3-4 mm/year (approximately 1.5 inches per decade).

- Sea Surface Temperatures (SSTs) have warmed over 5° C (9° F) over the waters west of Greenland since 1990 (Figure 1, to the right). This has caused the ice-free season to increase by over 60 days per year along the coast.

- The Greenland ice sheet has experienced conditions as warm as those today in the past. Lowell et al. (2007) found organic remains in eastern Greenland that had just been exposed by melting ice, and dated these remains at between A.D. 800 to 1014. Thus, this portion of Greenland was ice-free about 1000 years ago, and temperatures were presumably similar to today's. Erik the Red took advantage of this warm period to establish the first Norse settlements in Greenland around 950 A.D. However, the climate cooled after 1200 A.D., and the Norse settlements disappeared by 1550.

For more information, see our new Greenland feature on our expanding climate change page.

Jeff Masters

References
Lowell, T.V., et al., 2007, Organic Remains from the Istorvet Ice Cap, Liverpool Land, East Greenland: A Record of Late Holocene Climate Change,, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract C13A-04.

Stearns, L.A., and G.S. Hamilton, 2007, New States of Behavior: Current Status of Outlet Glaciers in Southeast Greenland and the Potential for Similar Changes Elsewhere, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract C13A-06.

Tedesco, M., "A New Record in 2007 for Melting in Greenland," EOS, 88:39, 2007, 383.

Climate Change

Christmas weather books and Storm Chaser book review

By: JeffMasters, 4:54 PM GMT on December 18, 2007

Storm Chaser: A Photographer's Journey ($23.10 from Amazon) takes the reader on a spectacular photographic journey through the U.S., documenting four seasons of our beautiful and violent weather. Author Jim Reed makes a business of weather photography, and has spent over 15 years chasing storms and documenting their awesome beauty and violent destructive power. The 191-page book would make a perfect Christmas coffee table book for that weather enthusiast (yourself?) in the family, and has great photos of tornadoes, hurricanes, hailstorms, blizzards, sunsets, and lightning. The book is mostly photos, but there are several riveting stories Reed tells. Most captivating is the story of his encounter with Category 4 Hurricane Charley as it pounded Punta Gorda, Florida in 2004. Reed miscalculated his time needed to get to shelter, and got caught in his vehicle on the road in the eyewall. Luckily, his videotaped farewell for mother and friends done during the height of the storm was not needed, as he was able to find shelter during the 4-minute passage of the eye. Reed also braved Hurricane Katrina from the beach front, and tells an abbreviated version of his dramatic encounter with the hurricane from Gulfport, Mississippi. I also recommend Hurricane Katrina Through the Eyes of Storm Chasers ($14.96 from Amazon) to read the full tale of his Katrina experience.

Storm Chaser: A Photographer's Journey has a few flaws. The quality of the writing is not quite as high as that of my favorite storm chaser book, the now dated 1996 Warren Faidley book, Storm Chaser: In pursuit of untamed skies (no longer in print, but available used). Reed's text doesn't match up with the photos presented on the pages in places, and he makes a number of unwarranted connections between global warming and extreme weather events. For example, he blames the June 22, 2003 fall of volley ball-sized hailstones in Aurora, Kansas on global warming. No single weather event can be attributed to climate change--all we can say is that the probabilities of some extreme weather events have increased. For example, the incidence of extreme precipitation events (the heaviest 1% of rain storms) has increased 20% over the U.S. in recent decades. No scientific papers have been published showing a link between tornadoes or hailstorms and climate change. That quibble aside, I heartily recommend Storm Chaser: A Photographer's Journey. The photos are fantastic. Three and a half stars out of four.

Best weather books published in 2007

Weather Photography:
Storm Chaser: A Photographer's Journey ($23.10 from Amazon).

Climate change:
Storm World: Hurricanes, Politics, and the Battle Over Global Warming by Chris Mooney ($17.16 from Amazon). See the realclimate.org review. I'll be posting a review of my own at some point.

General Weather:
Extreme Weather: A Guide and Record Book by Christopher Burt ($17.13 from Amazon). I hope to review this book soon.

Hurricanes:
Hurricane Almanac by Bryan Norcross ($11.04 from Amazon). See my review of the book.

Tornadoes:
Storm Warning: the Story of a Killer Tornado by Nancy Mathis ($16.32 from Amazon). See my review of the book.

Jeff Masters

Book and Movie Reviews

Winter grips North America

By: JeffMasters, 3:23 PM GMT on December 17, 2007

We've got a real winter on our hands in North America this December. The latest in series of storms that has pounded the continent left nearly a foot of snow over portions of Michigan, New York, Massachusetts, Maine, and Canada Sunday. Heavy snow collapsed the roof of a pharmacy in Boston, injuring one person yesterday. Heavy ice accumulations were a problem in Pennsylvania, where ice and high winds brought down the 800-foot high TV tower of WNEP-TV. A possible tornado associated with the storm's trailing cold front swept through Land 'O Lakes, Florida early Sunday morning, destroying a jail and flipping cars. No one was injured, and the inmates were moved to safety before the storm hit.


Figure 1. Departure of surface temperature from average for the period December 1-15, 2007. Note that the northern U.S. has seen below average temperatures, but the southern U.S. has seen above average temperatures. Temperatures across most of Europe and Asia have been much above average. Temperatures over ocean areas are not reliable in this data set, and should be ignored. Image credit: NOAA ESRL.

This winter's jet stream pattern
When this year's record sea ice melt in the Arctic occurred, I predicted another late arrival to winter over the Northern Hemisphere, because of all the extra heat and moisture the loss of sea ice would provide to the polar atmosphere. Well, winter arrived pretty much on time over North America. We've seen temperatures near average during the first half of December (Figure 1). However, almost all of Europe and Asia have seen a delayed start to winter. First half of December temperatures have been 3-6°C (5-10°F) above average across most of Europe, and even warmer over much of Asia. While the ski areas of the Alps have gotten much more bountiful snow than last winter, the lack of cold temperatures and snow is hurting the tourist industry in many regions, such as Finland. In Eastern Siberia, the lack of usual sea ice has led to temperatures up to 15°C (27°F) above average during the first half of December. The missing sea ice between Russia and Alaska has also brought unusual storminess and low pressure to the region during November and December. This may have deflected the position of the jet stream, bringing colder conditions to North America than the rest of the Northern Hemisphere. The current La Nina event and natural variability are also involved, and it is difficult to say which effect is mostly responsible for the current jet stream pattern.

What does the rest of December hold in store? Well, the latest 16-day forecast from the GFS model shows no major changes to the jet stream pattern. Expect a continuation of normal winter weather over North America, and much warmer than average conditions over Europe and Asia.

Jeff Masters

Winter Weather

Sunday's 'Noreaster

By: JeffMasters, 3:23 PM GMT on December 14, 2007

Sunday's 'Noreaster looks to be a wet one, thanks in part to Tropical Storm Olga. Visible satellite images show the remains of Olga continue to spin in the Western Caribbean, generating a bit of shower activity that may give a wet day to Mexico's Yucatan Peninsula on Saturday. Wind shear over Olga's remains is 40 knots and rising, so no redevelopment is expected. On Saturday, the progenitor of Sunday's 'Noreaster is expected to develop over the northern Gulf of Mexico. This storm will pull the remains of Olga into it, making for a very wet storm when it hits the Northeast U.S. Expect heavy snow amounts of 1-2 feet and significant ice accumulations to inland regions of Pennsylvania, New York, Massachusetts, New Hampshire, Vermont, and Maine. Rain appears to be the most likely type of precipitation at locations nearer the coast, such as Philadelphia and New York City. Boston will get a horrible mix of snow, sleet and rain, which could shut down Logan Airport for a time Sunday. Minor coastal flooding due to strong northeast winds is expected along the coast from New York City to Maine on Sunday. With some significant freezing rain coupled with strong winds expected in many regions, falling tree limbs will cause widespread power outages.

Consult the Northeast Weather blog for a more detailed analysis of this weekend's storm.

Jeff Masters

Winter Weather

Olga: deadliest December tropical storm ever; Northeast U.S. braces for storms

By: JeffMasters, 4:05 PM GMT on December 13, 2007

Tropical Storm Olga is gone, destroyed by high wind shear and dry air. The storm, only the fourth December tropical storm on record to hit land, is also the deadliest December tropical cyclone on record. At least 22 people have died due to flooding in its wake. One man was killed on Puerto Rico in a mudslide, two people died on Haiti due to flash floods, and at least 19 people died in the Dominican Republic. The only other December killer storm on record was Tropical Storm Odette, a 65-mph tropical storm that killed eight people in the Dominican Republic on December 7, 2003.

Most of the deaths in the Dominican Republic occurred in its second largest city, Santiago, when water was released from the Taveras dam upstream of the city in order to keep the dam from failing. Questions are being raised about why evacuations orders given several hours before the water release were not heeded, according the local Dominican Today newspaper. The tourist areas of the Dominican Republic were largely unaffected by Olga's rains, which were concentrated in regions of the northern part of the country.


Figure 1. Water is released from the Taveras dam during Tropical Storm Noel in late October 2007. Image credit: Wunderphotographer DRWeather.

Double whammy of winter storms for the Northeast U.S.
The Northeast U.S. is expected to receive a double helping of severe winter weather over the next few days. Today, a quick but intense winter storm is expected to dump 6-12 inches of snow across northern Connecticut, northern Rhode Island, and much of Massachusetts. A full-fledged 'Noreaster is expected Sunday, bringing heavy snow amounts of 1-2 feet and significant ice accumulations to inland regions of Pennsylvania, New York, Massachusetts, New Hampshire, Vermont, and Maine. Rain appears to be the most likely type of precipitation at locations nearer the coast, such as Philadelphia, New York City, and Boston. It is too early to be confident of this forecast, since minor changes in the storm's track will greatly influence the type of precipitation. Minor coastal flooding due to strong northeast winds is expected along the coast from New York City to Maine on Sunday.

Jeff Masters

Olga falling apart; big 'Noreaster coming Sunday

By: JeffMasters, 3:47 PM GMT on December 12, 2007

The hurricane season of 2007 is almost over (again!) Tropical Storm Olga's passage over the rough terrain of Hispaniola has considerably disrupted the circulation of the storm, and visible satellite loops show a poorly organized circulation with a few weak rain bands removed to the north and east of the center. Radar loops out of Gran Piedra, Cuba show disorganized patches of rain impacting eastern Cuba, western Haiti, and the southeastern Bahama Islands. Puerto Rico took the brunt of Olga's rains, with amounts exceeding eight inches common (Figure 1). Satellite estimates of rainfall over Hispaniola show maximum rainfall amounts of up to four inches thus far over the northern Dominican Republic and Haiti. Additional rains of 2-4 inches from Olga may cause localized flash flooding and mudslides, but Olga will cause nowhere near the chaos that the 10-25 inches of rain from Tropical Storm Noel did in late October.

Wind shear has increased to 30 knots over Olga, and water vapor satellite imagery shows that Olga is moving into some very dry air. These influences should destroy Olga by Thursday. The remnants of Olga may still bring heavy rains of 2-4 inches to the southeast Bahamas and eastern Cuba, and 1-2 inches to Jamaica and the Cayman Islands. The 00Z runs of the GFDL and HWRF computer models foresee that Olga will regenerate on Friday and threaten the north coast of Honduras on Sunday as a Category 1 hurricane, but this solution is not supported by the other models. Given Olga's current weak condition, it is unlikely there will be enough left of the storm on Friday to regenerate into anything.


Figure 1. Precipitation estimated from the Puerto Rico radar for Tropical Storm Olga.

Major 'Noreaster coming Sunday
All of the major computer models forecast that a major winter storm will track across the Ohio Valley on Saturday, then explode into a powerful 'Noreaster Sunday off the U.S. northeast coast. Heavy snow amounts of 1-2 feet and significant ice accumulations are possible in inland regions of the Northeast. Rain appears to be the most likely type of precipitation at locations nearer the coast, such as Philadelphia, New York City, and Boston. It is too early to be confident of this forecast, since minor changes in the storm's track will greatly influence the type of precipitation. Minor to moderate coastal flooding is possible along the coast from New York City to Maine on Sunday.

Ice storm in the Midwest
I haven't found the opportunity to say much about the remarkable ice storm that has paralyzed much of Oklahoma, Kansas, Missouri, and surrounding regions this week, as I've been busy talking about Olga and trying to keep up on the latest in climate change science at the American Geophysical Union Conference here in San Francisco. The wunderphotos posted by people to the web site have been truly astounding, chilling, and beautiful, and I thank all of you who posted photos.

I'll have a update Thursday morning.

Jeff Masters

Olga pounds Puerto Rico; major 'Noreaster coming Sunday

By: JeffMasters, 3:19 PM GMT on December 11, 2007

The hurricane season of 2007 is definitely not over! Subtropical Storm Olga is the 17th December named storm to develop in the Atlantic since record keeping began in 1851, and only the fourth December named storm to hit land (Figure 1). Seven of the 17 December storms have occurred since 1995. Eight of the December storms have been hurricanes, with a Category 2 hurricane in 1925 being the only December storm to hit the mainland U.S.


Figure 1. Tracks of all Atlantic named storms that have formed in December.

As seen on visible satellite loops, the heavy thunderstorm activity associated with Olga is displaced 100-200 miles to the north of the center. This is one of the hallmarks of a subtropical storm. The difference is not important, as the winds and rain are similar for both types of storms. Long range radar out of Puerto Rico clearly shows the circulation of Olga and some well-organized bands of rain. Rain is the major threat from Olga, and amounts of 3-6 inches have already fallen over northern Puerto Rico, causing flash flooding and mudslides. Heavier rain amounts of over eight inches have fallen on ocean areas to the north of Puerto Rico (Figure 2), and rainfall amounts of up to 10 inches may hit the regions of the Dominican Republic hard hit by Tropical Storm Noel just six week ago. Haiti is also at risk of heavy rains that might cause life-threatening flash floods and mud slides.


Figure 2. Latest precipitation estimate from the Puerto Rico radar.

Wind shear, which dropped to about 15-20 knots Monday evening, has increased to 20-30 knots today. This higher shear, combined with Olga's passage over the rough terrain of Hispaniola, should be enough to tear the storm apart. The remnants of Olga may still bring heavy rains of 2-4 inches to Jamaica and eastern Cuba Wednesday and Thursday. None of the computer models foresee that Olga will survive to become a tropical storm in the Western Caribbean. The Hurricane Hunters are not on call to fly Olga.

Major 'Noreaster coming Sunday
Both the GFS and ECMWF models are forecasting that a major winter storm will track across the Ohio Valley on Saturday, then explode into a powerful 'Noreaster on Sunday with a central pressure of 970-980 mb off the U.S. northeast coast. Heavy snow amounts of 1-2 feet and significant ice accumulations are possible in inland regions of the Northeast. Locations nearer the coast, such a Philadelphia, New York City, and Boston may mostly get rain, but it is too early to be confident of this forecast. Minor to moderate coastal flooding is possible along the coast from New York City to Maine on Sunday.

I'll have a update Wednesday morning.

Jeff Masters

A rare December named storm for the Atlantic: Olga

By: JeffMasters, 3:49 AM GMT on December 11, 2007

The hurricane season of 2007 is definitely not over! Subtropical Storm Olga is the 17th December named storm to develop in the Atlantic since record keeping began in 1851. Seven of these 17 storms have occurred since 1995.

As seen on visible satellite loops, the heavy thunderstorm activity that was displaced 100-300 miles to the north of the center has now wrapped closer to the center of Olga's circulation. This is the sign of a system evolving to be a tropical storm. However, an upper level low pressure system over the Virgin Islands is dumping some cold air into the storm, and Olga is still technically a subtropical storm. The difference is not important, as the winds and rain are similar for both types of storms. Long range radar out of Puerto Rico clearly shows the circulation of Olga and some steadily organizing bands of rain. Rain is the major threat from Olga, and amounts of 3-4 inches have already fallen over northern Puerto Rico, and a Flood Watch has been posted for much of the island. Heavier rain amounts of over six inches have fallen on ocean areas to the north of Puerto Rico (Figure 1), and rainfall amounts of up to 10 inches may hit the regions of the Dominican Republic hard hit by Tropical Storm Noel just six week ago. Haiti is also at risk of heavy rains that might cause life-threatening flash floods and mud slides.


Figure 1. Latest precipitation estimate from the Puerto Rico radar.

Wind shear, which dropped to about 15-20 knots this evening, is low enough to allow some slow strengthening Tuesday. By Wednesday, rising wind shear, plus passage over the rough terrain of Hispaniola, should be enough to tear Olga apart. The remnants of Olga may still bring heavy rains of 2-4 inches to Jamaica and eastern Cuba Wednesday and Thursday. None of the computer models foresee that Olga will survive to become a tropical storm in the Western Caribbean. The Hurricane Hunters are not on call to fly Olga.

I'll have a update Tuesday morning by 11am EST.

Jeff Masters

Puerto Rico braces for a December surprise: 94L

By: JeffMasters, 3:49 PM GMT on December 10, 2007

The hurricane season of 2007 over may not be quite over. An area of disturbed weather about 200 miles east of Puerto Rico, designated Invest 94 by NHC, may develop into a subtropical or tropical storm. The system developed a surface circulation near 18N 63W this morning, as seen on visible satellite loops. The heavy thunderstorm activity is displaced 100-300 miles to the north of the center, making 94L a subtropical system. Long range radar out of Puerto Rico shows some disorganized bands of rain affecting the Virgin Islands, Puerto Rico, and surrounding waters, but these bands are not well-organized. Water temperatures in the region are about 26-27° C, which is barely warm enough to support formation of a tropical storm. Last evening's 8:12 pm EST QuikSCAT pass showed top winds of 30-35 mph. Unfortunately, this morning's QuikSCAT and ASCAT passes both missed 94L. Wind shear is 20-25 knots over the disturbance, which is too high to allow anything but slow development. However, 94L is very close to being a subtropical depression, and only a slight increase in organization would be needed to call it a subtropical depression.


Figure 1. Latest satellite image of Invest 94.

Here's what NHC had to say about the disturbance:

Special tropical disturbance statement
1100 am EST Mon Dec 10 2007

Satellite images and surface reports indicate that a closed surface circulation has developed in association with the broad area of low pressure now centered about 200 miles east of Puerto Rico. Shower activity with the low remains disorganized...however...with the strongest thunderstorms located a couple hundred miles north and northeast of the center. While a tropical or subtropical cyclone could still form during the next 24 hours...upper-level winds are expected to become gradually less favorable for development over the next couple of days. Regardless of whether the low develops further...it could produce heavy squalls and gusty winds of near gale force across the Virgin Islands and Puerto Rico later today and tonight as it moves westward or west-southwestward at about 20 mph. Heavy rains over Puerto Rico and Hispaniola could cause life-threatening flash floods and mud slides...and interests in these areas should continue to monitor the progress of this system.

Wind shear is expected to remain in the 20-25 knot range Monday, which may be low enough to allow 94L to organize into a subtropical depression or subtropical storm today. Regardless, 94L will affect Puerto Rico today and tonight similar to how a tropical depression would, with sustained winds of 30 mph gusting to 45 mph, and heavy rains up to 5 inches. On Tuesday, these conditions will spread to the Dominican Republic and Haiti. The high terrain of Hispaniola should disrupt 94L, and wind shear is also expected to increase. By Wednesday, 94L will probably bring heavy rain to Jamaica. The GFDL model indicates that wind shear will drop and 94L will organize into a tropical storm on Wednesday. The model forecasts that the storm will intensify and move west-southwest to threaten the northern coast of Honduras on Friday. None of the other models develop 94L, though. Wind shear is expected to be low enough to support tropical storm formation in the Western Caribbean on Wednesday-Thursday, if there is anything left of 94L after its encounter Tuesday with Hispaniola. The Hurricane Hunters are not on call to fly 94L at all, and I don't expect this storm will survive intact enough to become a tropical storm in the Western Caribbean later this week.

I'll have a update later today.

Jeff Masters

Hurricane season not over?

By: JeffMasters, 4:09 AM GMT on December 10, 2007

Is the hurricane season of 2007 over? An area of disturbed weather, designated Invest 94 by NHC, has developed about 400 miles east of Puerto Rico, and is moving west at 15-20 mph. The disturbance shows some modest organization on satellite imagery (Figure 1), with decent heavy thunderstorm activity, and an upper-level outflow channel to the north. Water temperatures in the region are about 26° C, which is right at the limit of what can support formation of a tropical storm. This evening's 8:12 pm EST QuikSCAT pass showed top winds of 30-35 mph, but no evidence of a surface circulation, and not much of a wind shift at the surface. Wind shear is 20-25 knots over the disturbance, which is too high to allow anything but slow development.


Figure 1. Latest satellite image of Invest 94.

Here's what NHC had to say about the disturbance:

1030 PM EST Sun Dec 9 2007

The area of disturbed weather associated with a broad area of low pressure centered about 425 miles east of Puerto Rico remains fairly well-organized...but satellite images and surface observations suggest that this system has not developed a closed circulation yet. This system is moving westward at 15 to 20 mph and is producing heavy squalls with gale force winds to the north of the shower activity. Environmental conditions appear to be favorable for some development and a tropical or subtropical storm could form during the next 24 hours. Interests in the northern Leeward Islands...the Virgin Islands...Puerto Rico...Hispaniola...and the eastern Bahamas should monitor the progress of this system.

None of the models develop the disturbance, but they do indicate that wind shear will remain near 20 knots through Monday night. This may allow 94L to stay organized enough to bring heavy rain and wind gusts up to 40 mph to Puerto Rico Monday night and on Tuesday morning to the eastern Dominican Republic. The disturbance is moving fast enough, about 20 mph, that the chances for serious flooding like Tropical Storm Noel brought to the region are low. By Tuesday, the models are showing an increase in wind shear to 30 knots, which should prevent further development. If there's anything left of 94L by Thursday, when it reaches the Western Caribbean, wind shear is expected to drop to 15 knots, and the system has a better chance of developing. I don't expect 94L will ever develop into a tropical storm, though.

I'll have a update Monday morning.

Jeff Masters

Hurricane season of 2008 forecast to be moderately more active than average

By: JeffMasters, 5:09 PM GMT on December 07, 2007

It's going to be a modestly more active than average Atlantic hurricane season in 2008, according to the latest seasonal forecast issued by Dr. Bill Gray and Phil Klotzbach of Colorado State University (CSU) today. The CSU team is calling for 13 named storms, 7 hurricanes, 3 intense hurricanes, and an ACE index 20% above average (Accumulated Cyclone Energy (ACE) is a measure of the total destructive power of a hurricane season, based on the number of days strong winds are observed). An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The CSU forecast calls for a 15% above average chance of a major hurricane hitting the U.S. The odds for a major East Coast hurricane are put at 37% (a 31% chance is average), and odds for the Gulf Coast are 36% (30% chance is average). The CSU team predicts that the current moderate La Nina event will weaken by the 2008 hurricane season, but still contribute to lower than average values of wind shear. In addition, warm sea surface temperatures are likely to continue in the tropical and North Atlantic during 2008, due to the fact that we are in a positive phase of the Atlantic Multidecadal Oscillation (AMO), which began in 1995.

The forecasters examined the observed atmospheric conditions and ocean temperatures in October-November 2007, and came up with a list of five past years that had a similar combination of a moderate La Nina event, near average tropical Atlantic sea surface temperatures (SSTs), and warm far North Atlantic SSTs. Expect 2008 to be similar to the average of these five analogue years, they say. The five years were 2000 (14 named storms, 8 hurricanes, 3 intense hurricanes), 1999 (12, 8, and 5 of the same), 1989 (11, 7 and 2), 1956 (8, 4 and 2), and 1953 (14, 6 and 4). Hurricane Hugo of 1989 (Category 4) was the strongest hurricane to hit the U.S. in these five analogue years.


Figure 1. Accuracy of long-range forecasts of Atlantic hurricane season activity performed by Bill Gray and Phil Klotzbach of Colorado State University (colored squares) and TSR (colored lines). The skill is measured by the Mean Square Skill Score (MSSS), which looks at the error and squares it, then compares the percent improvement the forecast has over a climatological forecast of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TS=Tropical Storms, H=Hurricanes, IH=Intense Hurricanes, ACE=Accumulated Cyclone Energy, NTC=Net Tropical Cyclone Activity. Image credit: TSR.

How good are these December hurricane season forecasts?
For the first time, the CSU team presents detailed information informing users of the accuracy of their December forecasts. Past December forecasts by CSU have had no skill, and I've criticized them for not clearly stating this. I applaud their efforts in today's forecast, where it says in the 2nd paragraph of the abstract, "These real-time operational early December forecasts have not shown forecast skill over climatology during the period 1992-2007". Later in the report, they show that the correlation coefficient (r squared), a standard mathematical measure of skill, is near zero for their December forecasts. As an example of this lack of skill, consider the figures presented in the November 2007 verification report. This report stated that 65% of their December forecasts between 1999 and 2007 correctly predicted whether the coming hurricane season would be above or below normal, for forecasts of number of named storms, hurricanes, intense hurricane, and number of days these storms are present. That 65% figure sounds pretty good, but is it skillful? To answer that question, I tallied up how an almost zero-skill forecast would have done over the same period. My almost zero-skill forecast simply assumed that since we are in an active hurricane period that began in 1995, every hurricane season will have an above normal number of named storms, hurricanes, intense hurricanes, and number of days storms are present. The result? My almost zero-skill forecast got it right 65% of the time, exactly the same as the CSU December forecast.

Another way to measure skill is using the Mean Square Skill Score (MSSS), which looks at the forecast error and squares it, then compares the percent improvement the forecast has over a climatological forecast of 10 named storms, 6 hurricanes, and 2 intense hurricanes (Figure 1). The skill of the December forecasts issued by both CSU and Tropical Storm Risk, Inc. (TSR) have averaged near zero since 1992. Not surprisingly, the forecasts get better the closer they get to hurricane season. The TSR forecasts show more skill than the CSU forecasts, but it is unclear how much of this superiority is due to the fact that TSR issues forecasts of fractional storms (for example, TSR may forecast 14.7 named storms, while CSU uses only whole numbers like 14 or 15). TSR does an excellent job communicating their seasonal forecast skill. Each forecast is accompanied by a "Forecast Skill at this Lead" number, and they clearly define this quantity as "Percentage Improvement in Mean Square Error over Running 10-year Prior Climate Norm from Replicated Real Time Forecasts 1987-2006."

The June and August forecasts from CSU, TSR, and NOAA show some modest skill, and are valuable tools for insurance companies and emergency planners to help estimate their risks. The key problem with earlier forecasts is that the El Nino/La Nina atmospheric cycle that can dominate the activity of an Atlantic hurricane season is generally not predictable more than 3-6 months in advance. For example, none of the El Nino forecast models foresaw the September 2006 El Nino event until April or May of 2006. Until we can forecast the evolution of El Nino more than six months in advance, December forecasts of Atlantic hurricane activity are merely interesting mental exercises that don't deserve the media attention they get. There is hope for the December forecasts, since Klotzbach and Gray (2004) showed that their statistical scheme could make a skillful forecast in December, when applied to 50 years of historical data. However, these "hindcasts" are much easier to make than a real-time forecast. For example, before 1995, it was observed that high rainfall in the Sahel region of Africa was correlated with increased Atlantic hurricane activity. This correlation was used as part of the CSU forecast scheme. However, when the current active hurricane period began in 1995, the correlation stopped working. Drought conditions occurred in the Sahel, but Atlantic hurricane activity showed a major increase. The CSU team was forced to drop African rainfall as a predictor of Atlantic hurricane activity.

Hotel owner threatens to sue Bill Gray for bad forecasts
Central Florida's most famous hotel owner, Harris Rosen, has threatened to sue Bill Gray because his bad forecasts have cost Florida billions of dollars in tourist revenue, according to a story published in November 2007 by WKMG Orlando. I think the record-breaking hurricane seasons of 2004 and 2005 had more to do with lost tourist revenue than any forecast by Bill Gray, so this is a rather ridiculous threat. However, these sorts of ugly accusations are the inevitable result of a culture where seasonal hurricane forecasts, which are not very good, are excessively hyped by both the forecasters and the media. The forecasters have set them selves up for such shrill condemnations by putting out these very public forecasts, complete with press conferences, but not properly emphasizing the uncertainties and low skill of their forecasts. By clearly stating their lack of forecast skill, the CSU team's December 2007 forecast is a great step towards improving this situation. The public needs to know that these December forecasts as yet have no skill, and are unworthy of the media attention they get.

References
Klotzbach, P.J., and W.M. Gray, "Updated 6-11 Month Prediction of Atlantic Basin Seasonal Hurricane Activity," Weather and Forecasting 19, Issue 5, October 2004, pp 917-934.

Next blog
Next week, I'll be blogging from San Francisco. It's time for the world's largest scientific meeting on climate change, the annual meeting of the American Geophysical Union.

Jeff Masters

QuikSCAT satellite showing its age; ASCAT satellite helping out

By: JeffMasters, 2:48 PM GMT on December 05, 2007

The now-famous QuikSCAT satellite, which measures winds at the ocean surface world-wide twice per day, was launched in 1999, and has now exceeded its expected lifetime by several years. A reminder of this satellite's age came during the week of November 21-28, when one of the cells on the satellite's battery went bad, forcing engineers to shut off data gathering on the satellite for about 10-15 minutes as it crossed over land in the Arctic. As a result, QuikSCAT provided only half of its usual data on winds and sea ice in the Arctic during that week. Fortunately, engineers were able to swap in a spare battery cell on November 28, and QuikSCAT is now back at full operation. This is good news, since QuikSCAT is a huge help for marine forecasts, sea ice forecasts, and predictions of tropical storms.

QuikSCAT now has help. An important new source of QuikSCAT-like data has been made available by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT). They launched their first polar-orbiting satellite, Metop-A, in October 2006, and declared the satellite ready for routine operations as of May 2007. This satellite carries a scatterometer called ASCAT which, like QuikSCAT, measures the winds at the ocean surface. ASCAT doesn't "see" the Earth's surface as well as QuikSCAT can--ASCAT sees chunks of the surface 25 km by 25 km, while QuikSCAT has a resolution twice as good--12.5 km. In addition, ASCAT only sees 60% of what QuikSCAT sees of the Earth's surface--QuikSCAT sees a swath of ocean 1800 km wide, while ASCAT sees two parallel swaths 550 km wide, separated by a 720 km gap. I found it frustrating to use ASCAT much this hurricane season, since it seemed that the passes missed the center of circulation of a storm of interest about 75% of the time.


Figure 1. Comparison of the coverage pattern of the QuikSCAT and ASCAT satellites, from December 4, 2007. Image credit: NOAA.

However, ASCAT has an important advantage--it can measure ocean surface winds where heavy rain is occurring, something QuikSCAT cannot. Both instruments carry an "active" radar (also called a scatterometer)--an instrument that emits a pulse of microwave energy that bounces off the ocean surface and returns to the satellite. The amount of microwave energy bounced back to the instrument is inversely proportional to how rough the sea surface is, and one can compute the wind speed and direction at the ocean surface based on this information. QuikSCAT uses microwave energy with a wavelength of about 2 cm (Ku-band), which is significantly affected by heavy rain. Microwave radiation from ASCAT uses a wavelength of about 5 cm (C-band), which is much less affected by rain. Thus, ASCAT can retrieve winds more accurately in the heavier precipitation environments such as those found in hurricanes. However, QuikSCAT does have finer spatial resolution and better sensitivity to high winds than ASCAT. Another minor advantage of ASCAT is that the winds across the entire swath of ocean it looks at are of uniform accuracy. QuikSCAT, on the other hand, has a bit larger errors at the edge of its 1800 km-wide swath, and in the middle, making it more difficult to interpret the data in some cases.

QuikSCAT data is routinely ingested into all of the major computer models that forecast hurricanes. ASCAT data is not yet used in this way, since ASCAT is currently still in its calibration and validation phase. However, by the 2008 hurricane season, ASCAT data will probably be used in this fashion. Having ASCAT to complement QuikSCAT will be a big help to NHC forecasters, particularly for those storms far out at sea where the Hurricane Hunters cannot reach.

ASCAT data is available from the ASCAT web page. QuikSCAT expert Dr. Paul Chang of NOAA also has ASCAT data available on his NOAA Marine Observing Systems web page.

Next blog
This Friday, the Colorado State University team issues its first forecast for the 2008 Atlantic hurricane season. I'll present an analysis of the forecast Friday afternoon.

Jeff Masters

Huge storm pounds Pacific Northwest with hurricane force winds

By: JeffMasters, 12:36 AM GMT on December 04, 2007

A powerful Pacific storm smashed ashore along the Oregon, Washington, and British Columbia coasts Monday, bringing hurricane force winds, torrential rains, and widespread flooding to the coast. Wind gusts over hurricane force (74 mph) were common along the coast, and one location, the aptly named Destruction Island in Washington, had sustained hurricane force winds (74 mph), with gusts to 93 mph. Winds gusting to 76 mph generated seas up to 48 feet high off the Oregon coast, and buoy 46050, 23 miles west of Newport, was torn from its mooring by 40 foot seas. Debris flow warnings have been posted for the steep mountain areas of the Oregon Coast Range near Tillamook. Debris flows are dangerous rapidly moving landslides. Rainfall amounts exceeding ten inches in the past day and a half have been measured in the North Oregon Coast Range. Rainfall amounts over a foot were estimated by the Seattle and Portland, OR radar (Figure 1).


Figure 1. Total rain from the Portland, OR radar for the Dec 3-5, 2007 storm.

Wind gusts exceeding hurricane force (74 mph) measured in OR and WA:

... Washington coast...
Cape Disappointment... ... ... ... ... ... .. 104 mph
Destruction Island... ... ... ... ... ... ... 93 mph
Toke Point (north end of Willapa Bay).. 75 mph

... North Oregon coast...
Bay City (near Tillamook)... ... ... ... ... 129 mph
Cape Meares (elev. 1500 ft)... ... ... ... 114 mph before power loss
Rockaway Beach... ... ... ... ... ... ... ... 104 mph
Tillamook Bay tide gage... ... ... ... ... 100 mph
Astoria (west slope)... ... ... ... ... ... 86 mph (sust. 45-50 mph)
Clatsop Spit... ... ... ... ... ... ... ... ... 86 mph (sust.70 mph)
Astoria Airport... ... ... ... ... ... ...... 85 mph
Garibaldi... ... ... ... ... ... ... ... ... ... 81 mph
Youngs Bay... ... ... ... ... ... ... ... ... .. 80 mph
Cannon Beach... ... ... ... ... ... ... ... ... 80 mph
Tillamook (downtown)... ... ... ... ... ... 75 mph
Tillamook Airport... ... ... ... ... ... ... 74 mph

... Central Oregon coast...
Lincoln City... ... ... ... ... ... ... ... ... 125 mph
Yaquina Hwy 101 bridge (Newport) ... ... 88 mph (sust. 45-50 mph)
Lincoln City (other report)... ... ... ... 85 mph
Newport Airport... ... ... ... ... ... ... ... 83 mph (sust. 58 mph)
Newport Jetty... ... ... ... ... ... ... ... .. 82 mph
Sea Lion Caves... ... ... ... ... ... ... ... . 81 mph (sust. 40-45 mph)
Agate Beach... ... ... ... ... ... ... ... ... . 78 mph (lost power)
Hatfield Science Center... ... ... ... ... . 75 mph

... Oregon Coast Range...
Mt. Hebo... ... ... ... ... ... ... ... ... ... . 91 mph
Cedar RAWS... ... ... ... ... ... ... ... ... .. 74 mph

... Cascade foothills...
Sugarloaf Mtn (SW of Oakridge)... ... ... 81 mph (sust. 35-40 mph)

... Cascades...
Timberline (elev. 7001 ft)... ... ... ... . 99 mph (sust. 60 mph)
Govt Camp Ski Bowl... ... ... ... ... ... ... 90 mph

The forecast
The storm, with a central pressure of 965 mb, is expected to move ashore Tuesday morning over the British Columbia coast and weaken. The strongest winds and heaviest rain have already past for the coast, but the inland Cascade Mountain range will see another 4-6 inches of rain by Tuesday afternoon. Flooding is possible Tuesday on all the rivers in western Washington and Oregon.

Jeff Masters

Winter 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