Dr. Jeff Masters' WunderBlog

The 6 lost Hurricane Hunter missions, Part III: Typhoon Doris, 1953

By: JeffMasters, 1:43 PM GMT on June 29, 2009

The tropics are quiet right now, as the "invest 93" disturbance over the Yucatan Peninsula has dissipated, and no computer models are showing any Atlantic tropical storm formation over the next seven days. Thus, it's a good time to continue with my series on the six typhoon/hurricane hunter missions that never returned.

The third typhoon hunter mission lost occurred on December 16, 1953, during a penetration by a Navy PB4Y-2S (Bu No 59176) into Typhoon Doris. The aircraft was part of a six plane squadron, VJ-1/VW-3, COMFAIRGUAM, based at the Naval Air Station in Agana, Guam (VJ-1 was formed in 1952 at NAS Sand Point, Seattle, Washington, and the name later changed to VW-3). The PB4Y-2S aircraft made its initial penetration into Doris' eye at 200 - 300 feet. As the aircraft radioed back a report at 2245Z, the transmission suddenly ceased. The plane was never heard from again. At the time, Doris was a Category 2 typhoon with sustained winds of 95 knots (110 mph). Again, given the low penetration altitude of the aircraft, it is likely that a downdraft carried the plane into the sea. It's pretty common to get downdrafts that will cause a 300 foot loss of altitude, despite the attempts of the pilot to climb with full power to the engines.

A nine-day long search and rescue operation failed to find any trace of the missing aircraft. Tragically, two aircraft involved in the search and rescue mission crashed, killing 39 more people. The first of these planes was a R4D (DC 3) that crashed into the crater of Agrihan Island, Mariannas, killing all ten crew members. This aircraft was not from the NAS Agana, Guam group. In addition, a B-29 based at Anderson AFB had an engine fail while looking for the missing typhoon hunter aircraft, and crashed during landing into an officer's housing area on Guam. A total of 29 people died in the crash, including at least 11 of the 16 crew members on the aircraft.

The nine crewmen lost during the flight into Typhoon Doris were:

Pilot J. W. Newhall age 39
Co-pilot S. B. Marsden, age 29
Lt. Cmdr. D. Zimmerman Jr., age 35
Ltjg. F. Troescher Jr., age 26
AL1 F. R. Barnett, age 26
AD1 J. N. Clark, age 32
AD3 E. L. Myer, age 20
AL2 N. J. Stephens, age 23
AO3 A. J. Stott, age 23

I got in contact with Austen Doolittle, who was operating the radio set in Guam when the transmission inside Typhoon Doris from the plane's radio operator, Norm Stephens, suddenly stopped. Austen recalled:

Jeff, I appreciate receiving your email, Earl Beech and I were at our second reunion in 55 years the 4th to 8th of May at Pensacola FL. Had a great time. Its important to the members of the VJ1/VW3 to make people aware of what we were doing so many years ago as 19 and 20 year old young sailors. I lost three of my best navy friends in that accident, and to this day I still wonder about the happenstance of my being on base radio that day and receiving the POMAR reports from Norm Stephens. There was an ability to recognize the hand or keying of people you knew, and I know that Norm Stephens was keying that last message to me. When he cut off I knew something had happened, and it really shook me up, and I tried to raise the plane many times until I knew it was not possible. I still have many pictures of Norm, Don Stott and Jim Clark in my album. Thanks for what you are doing, I really appreciate it. I've had a long and fruitful life since then, but I'll never forget that day, and still wonder why I was so lucky.

Austen



Figure 1. Painting of a Navy PB4Y-2S "Privateer" aircraft flown by the VJ-1/VW3 Squadron. Image credit: USS Whitehurst DE-634 web site. Several stories by members of the VJ-1/VW3 Squadron concerning the Typhoon Doris disaster are posted on the web site.

Other sources: http://www.vpnavy.com/vj1_notice.html

Past posts in this series:
October 1, 1945 typhoon
Typhoon Wilma, 1952


I'm back from vacation now, and my next blog post will be Wednesday, when I'll present the July Atlantic hurricane outlook.

Jeff Masters

Updated: 12:28 PM GMT on July 01, 2009

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Much Ado About Nothing: Invest93L

By: JeffMasters, 12:29 PM GMT on June 28, 2009

Hi, this is Rob Carver, again filling in for Jeff Masters.

Invest93L is still present as of the 8am EDT Tropical Weather Outlook, but I'm extremely doubtful that it will reach even tropical depression status.

Invest93L's presentation on satellite imagery does not project the image of a strengthening storm. Convection, what there is of it, appears to be anchored over the Yucatan Straits and is not following the low-level circulation center. Also, microwave imagery indicates that the convection is weak, with relatively low rainfall rates.

It is worth noting that even if more convection forms after the circulation center moves into the Gulf of Mexico, there isn't much time for the storm to strengthen. By Tuesday evening, both the NAM and GFS 06Z model runs bring a weak front down into the Gulf, raising wind shear to the point that would dissipate Invest93L.

So, after considering the above, it's my opinion that Invest93L is not likely to intensify and will dissipate in a day or so.

Rob Carver

Hurricane

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A late look at Invest93L

By: JeffMasters, 6:52 AM GMT on June 27, 2009

Hi everybody, this is Rob Carver, R&D Scientist for Wunderground, filling in for Jeff Masters.

Summary of the situation

In the Tropical Weather Outlook NHC has tagged a tropical wave in the NW Caribbean Sea as Invest93L and believes that it has a 30-50% chance of developing into a tropical cyclone in the next 48 hours. As of now (11 PM PDT, June 26), the Hurricane Hunters are scheduled to investigate this area on June 28. The track models have Invest93L moving through the Yucatan Straits into the Gulf of Mexico. After that, most of the models take the cyclone north and east making landfall along a wide swath of Florida's Gulf Coast on Wednesday of next week. The intensity models predict that at landfall, the system will be a weak Category 1 hurricane or strong tropical storm.


Figure 1. Plot of upper-level wind shear from CIMSS

Wind Shear Aloft

The wind shear patterns are favorable for intensification of Invest93L if it can make it through the Yucatan Straits. Figure 1 shows that currently, Invest93L is an unfavorable environment, with shear > 20 knots. However, north of the Yucatan Straits and SW of Florida, the shear drops to a favorable 5 knots. Both the GFS and NAM predict that that this shear pattern will be fairly constant over the next several days. Also, the water temperatures in the Gulf of Mexico are either normal or slightly above normal, so that will be favorable for storm development.

What happens next?
If Invest93L can survive long enough to get in the Gulf of Mexico, then I believe it can develop into TS Ana, the first named storm of the year. However, survival is not guaranteed, the convection around Invest93L is not that persistent. That said, people with interests along the coast of the Gulf of Mexico should keep an eye on this storm this weekend and into the early part of the next week.

Rob Carver

Hurricane

Updated: 6:25 PM GMT on August 19, 2011

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The 6 lost Hurricane Hunter missions, Part II: Typhoon Wilma, 1952

By: JeffMasters, 2:58 PM GMT on June 26, 2009

Dr. Masters is on vacation this week, so we're posting some blogs he wrote before hitting the road.

The second Hurricane Hunter mission that didn't make it back was the only flight lost in a Category 5 storm. On October 26, 1952, an Air Force WB-29 aircraft knick-named "Typhoon Goon II" (44-69770), making a low-level penetration of Typhoon Wilma, went down 300 miles east of Leyte in the Philippines. The aircraft was attached to the 54th Weather Reconnaissance Squadron on Guam. The original "Typhoon Goon" was Aircraft 45-21838, which was stationed on Guam from January 1948 until December 1950, during which time she flew at least 25 typhoon missions. When Aircraft 770 arrived on Guam in January of 1951, she was given the name "Typhoon Goon II" to keep the tradition alive. The crew's last radio message indicated they were close to the eye and were attempting to make a low level fix. They reported that their radar altimeter had "burned out", and that they were going to fly in anyway, using just pressure altimetry to maintain the proper altitude. This was an extremely dangerous prospect, since Wilma was a Category 5 super typhoon with 185 mph winds at the time of penetration, and had a very sharp change in pressure near the eye. If the plane was attempting to fly at a constant pressure altitude, the pilot would have been forced to perform a steep descent in the eyewall. It is likely the aircraft hit a strong downdraft that carried them into the sea, or that severe turbulence caused the aircraft to go out of control, with insufficient time for the pilot to recover. The ten men lost on the mission were:

Maj Sterling L. Harrell
Capt Donald M. Baird
Capt Frank J. Pollack
1Lt William D. Burchell
1Lt Clifton R. Knickmeyer
MSgt Edward H. Fontaine
A1C Alton B. Brewton
A1C William Colgan
A1C Anthony J. Fasullo
A3C Rodney E. Verrill


Figure 1. The Air Force WB-29 named Typhoon Goon II, lost in Super Typhoon Wilma on October 26, 1952. Image credit: Arthur R. "Ray" Brashear, Air Reconnaissance Weather Association.

Sources: Personal communication, Bernie Barris, Air Reconnaissance Weather Association; "The Fireballs, an Unofficial History", by Robert A. Mann; "Flying the Weather", by Otho Spencer, 1996; Stars and Stripes 30 Oct 1952 page 1; New York Times, 9 Nov 1952 45:5.

Jeff Masters

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The 6 lost Hurricane Hunter missions, Part I: the Oct 1, 1945 typhoon

By: JeffMasters, 3:43 PM GMT on June 25, 2009

Dr. Masters is on vacation this week, so we're posting some blogs he wrote before hitting the road.

People have been flying into hurricanes and typhoons ever since 1943, when Colonel Joe Duckworth took a single engine AT-6 trainer aircraft into the "Surprise" hurricane off the coast of Texas. Hurricane hunting became safer with the introduction of sturdier 4-engine planes, but flying through the eyewall of any hurricane remains a dangerous occupation to this day--one that has claimed the lives of 53 crewmen of the six Hurricane Hunter flights that never made it back. Five of these flights were into Pacific typhoons, between the years 1945 and 1974. One Atlantic flight was lost, the 1955 Snowcloud Five mission into Category 4 Hurricane Janet. I will be running a six-part feature this hurricane season to honor the Hurricane Hunters that gave their lives in service to those us in the path of these great and deadly storms.

The first Typhoon Hunter plane was lost on October 1, 1945, when a Navy PB4Y-2 (BuNo 59415) went down in a Category 1 typhoon over the South China Sea. Pilot Lt(jg) Ralph Cook and Crew #34 of Patrol Bombing Squadron VPB119 took off from Clark Field in the Philippines at 0950 on October 1, 1945, to track and make half hourly in-flight reports on a typhoon at 22N 119E, between Taiwan and the Philippine Islands. Lt. Cook's fourth in-flight report was received by Base Radar at 1230, and gave his position as 20-06°N 120-08°E, altitude 9500 ft, heavy rain, visibility 50-200 yards, wind south at 40 knots, and slight turbulence. He was never heard from again. The entire area was searched thoroughly by a total of forty flights over a period of seven days. The wreckage of the airplane was finally found on Batan Island just north of Luzon in the Philippines (approximately 20-22°N 121-56°E). According to the Veteran's Administration grave locator data base, the crew remains are interred in a common grave at the Zachary Taylor National Cemetery in Louisville, KY. Of the six typhoon/hurricane hunter flights that never returned, this is the only one where the wreckage of the airplane was found. I speculate that since the aircraft was flying at relatively high altitude (9500 feet), they were not hurled into the ocean by a sudden downdraft. Instead, the airplane must have experienced a severe mechanical failure inside the typhoon. They were then forced to attempt an emergency landing on rugged Batan Island, which was being lashed by heavy rain and 40 - 60 mph winds at the time. The crewmen lost on the mission were:

Lt(jg) Ralph F. Cook A-V(N) USNR (Pilot)
Ens Harold E. Raveche A-V(N) USNR
Lt(jg) Oscar L. Smith A-V(N) USNR
AMM2c Kenneth D. Griffore USNR
ARM2c Darly B. Miler USNR
AOM1c James A Dugan USNR
ARM1c Royce A. Lamb USNR

Sources: "The Hurricane Hunters", a 1955 book by Ivan Tannehill; http://www.vpnavy.com/vp119_mishap_1940.html; personal communication, Dave Deatherage, son of Paul Deatherage, ART 1c, VPB119, 1944-45.


Figure 1. Six of the seven crew members of the first aircraft ever lost in a tropical cyclone, the October 1, 1945 loss of Navy PB4Y-2 (BuNo 59415). The photo of Ltjg Ralph Cook and Crew #34 of Patrol Bombing Squadron VPB119 was taken by Lt. Sylvester S. 'Bud' Aichele in late August or September of 1945. Cook and crew were a replacement crew that arrived at Clark Field on 22 August 1945. Left to right (standing: L.P. Hill, James A Dugan, Harold E. Raveche, Ralph F. Cook, C. F. Poland, Darly B. Miler, A. J. Kalton. Bottom row: N. P. Chamberlain, Royce A. Lamb, F. B. Arden, T. V. Wisely, Kenneth D. Griffore.


Figure 2. A PB4Y-2 aircraft in flight. These 4-engine patrol bombers were a modified version of the WWII B-24 bomber. They served as typhoon hunter aircraft from 1945 until the mid-1950s. Image credit: Max Crow, USS Whitehurst Association.

Jeff Masters

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U.S. vulnerability to sea level rise

By: JeffMasters, 4:04 PM GMT on June 23, 2009

In the last century, sea level rose 5 - 6 inches (13 - 15 cm) more than the global average of 7 inches (18 cm) along the U.S. Mid-Atlantic and Gulf Coasts, because coastal lands there are sinking. Over 50% of the U.S. coastline is vulnerable or highly vulnerable to sea level rise, according to the Coastal Vulnerability Index (CVI) developed by the United States Geological Survey (USGS). In the U.S., relative sea level rise (the combined effects of global sea level rise plus the fact the land is sinking) is highest along the Mississippi River Delta in Louisiana, where relative sea level rises of 3.2 ft (.98 meters) have been observed during the 20th century. This is one of the highest relative sea level rises in the world. According to the NOAA Tides and Currents sea level rise interactive tool, the U.S. tide gauges that have shown the highest rates of sea level rise over the past century are at Grand Island, LA (1.8 ft rise since 1947), Galveston, TX (1.1 ft since 1957), and Chesapeake Bay, VA (0.6 feet since 1975). Alaska and some areas along the Pacific Northwest coast are at low risk of sea level rise, because the relative sea level is actually falling at present. Land in these regions is rising as it recovers from removal of the weight of the great ice sheets that covered much of North America during the last Ice Age. For example, relative sea level at Kodiak Island, Alaska has fallen by 1.1 feet since 1975, despite the fact global sea level has been increasing.


Figure 1. Twentieth century annual relative sea-level rise rates in mm/year along the U.S. coast. The higher rates for Louisiana (9.85 millimeters [mm] per year, about 3.3 ft/century) and the mid-Atlantic region (1.75 to 4.42 mm per year, 0.6 - 1.4 ft/century) are due to land subsidence. Sea level is stable or dropping relative to the land in the Pacific Northwest, as indicated by the negative values, where the land is tectonically active or rebounding upward in response to the melting of ice sheets since the last Ice Age. Image credit: Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region (data from Zervas, 2001).

U.S. Coastal Vulnerability
The Coastal Vulnerability Index (CVI) takes into account six factors:

1) The geology of the coast. Barrier islands, river deltas, and marshes are the most vulnerable to erosion and sea level rise, while steep, rocky cliff shores are the least. Sheltered bays like Galveston Bay and Tampa Bay are less vulnerable than the exposed coasts. (Note, however, that hurricane storm surges are typically higher in sheltered bays, at least for slow-moving storms).

2) How steep the land near the coast is. Gently sloping lands are the most vulnerable. In the Gulf Coast region, the slope variable has the highest risk ranking along the Louisiana coast, the Texas coast north of Corpus Christi, and the southwest Florida coast.

3) The local rate of sea level rise. The sea level is rising faster along the western Gulf of Mexico than the eastern Gulf. The highest rates of sea-level rise in the Gulf of Mexico (and in the United States) are in the Mississippi delta region (10 mm/yr, or 1 inch/2.5 years).

4) The amount of shoreline erosion going on. Most of the U.S. coast is moderately or severely eroding, and very few areas are gaining (Figure 2).

5) The mean tidal range. Shores that have a large difference between low and high tide are less likely to get a significant storm tide--the height above mean sea level of the sum of the storm surge plus the tide. For example, in a region like Maine, which has a 12 ft range between low and high tide, a storm having a 9 ft storm surge will have a storm tide below local high tide for a quarter of a tidal cycle. Shores with a very narrow tidal range (e.g., the 2 ft tidal range common along the Texas and Louisiana Gulf Coast) will get a storm tide of 8 - 10 feet with the 9 ft storm surge in the above example. Shorelines with a narrow tidal range always get high storm tides regardless of when the storm surge hits.

6) How high the waves at shore are. Obviously, shores that experience higher wave heights are at greater risk. In the Gulf of Mexico, wave energy is highest along sections of the Texas coast and on the southern tip of the Mississippi delta.

Figure 2. Shoreline change around the United States based on surveys over the past century. All 30 coastal states are experiencing overall erosion due to natural processes (e.g., storms, sea-level rise) and human activity. If the shoreline is uncolored, no data was available. Image credit: USGS, 1985, and taken from Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region).

The Coastal Vulnerability Index (CVI) web page gives detailed maps of each section of the U.S. coast, along with specific reasons why each portion of the coast was assigned the ranking it got. A brief summary:

The Gulf Coast
The Gulf Coast has 55% of its length in the "very high" or "high" vulnerability range. Fully 41% of the coast falls in the "very high" range, far more than the 28% in that category along the Pacific coast and 23% along the Atlantic coast. The region around New Orleans is the most vulnerable region of the entire U.S. coast. The Florida Panhandle, as well as the West Florida coast, are at low to moderate risk because the land is not sinking much, wave heights are lower, and the slope of the land is relatively steep near the coast. The Texas coast is considered to be at a high to very high risk because of the relatively high mean wave height, sinking land, and shallow coastal slope.

The East Coast
The East Coast has 50% of its length in the "very high" or "high" vulnerability range. The highest vulnerability areas are typically high-energy coastlines where the regional coastal slope is low and where the major landform type is a barrier island. A significant exception to this is found in the lower Chesapeake Bay. Here, the low coastal slope, vulnerable landform type (salt marsh) and high rate of relative sea-level rise combine for a high CVI value. The coastline of northern New England, particularly Maine, shows a relatively low vulnerability to future sea-level rise. This is primarily due to the steep coastal slopes and rocky shoreline characteristic of the region, as well as the large tidal range.

The Pacific Coast
The Pacific Coast has 50% of its length in the "very high" or "high" vulnerability range. Areas of very high vulnerability include the San Francisco - Monterey Bay coast and in southern California from San Luis Obispo to San Diego, where the coast is most highly populated. The highest vulnerability areas are typically lower-lying beach areas. The low risk, least vulnerable areas generally occur at rocky headlands along cliffed coasts where the coastal slope is steep, relative sea-level is falling, tide range is large, and wave energy is lower. Examples of these areas are the northern coast of Washington, Monterey, and Cape Mendocino, California.


Figure 3. The Coast Vulnerability Index (CVI) for the U.S.

References
Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region.

National Assessment of Coastal Vulnerability to Sea-Level Rise: Preliminary Results for the U.S. Gulf of Mexico Coast (USGS, 2000).

Jeff Masters

Climate Change Sea level rise

Updated: 5:59 PM GMT on December 01, 2011

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Dust forecast for the 2009 Atlantic hurricane season

By: JeffMasters, 6:58 PM GMT on June 20, 2009

There will be less African dust than usual over the tropical Atlantic during this year's hurricane season, according to a new experimental dust forecast issued by Dr. Amato Evan of the University of Wisconsin. Dr. Evan used a statistical model that correlated levels of dust activity in past years with rainfall over the Sahel region of Africa and a natural regional wind pattern known as the North Atlantic Oscillation (NAO). He forecasts that dust levels over the Main Development Region (MDR, 8 - 20°N & 15 - 65°W) for Atlantic hurricanes during this year's hurricane season will be similar to last year's below-average levels, thanks in large part to plentiful rains over the Sahel region of Africa during the 2008 rainy season (Figure 1). However, the dust levels expected this year do not approach the record lows seen in 1994 and 2005. Dust forecasts made in May or June are skillful going out five months, with a skill 11 - 16% better than a "no-skill" forecast using climatology.


Figure 1. Rainfall over the Sahel region of Africa was generally 50 - 100 mm (2 - 4 inches) above average during the 2008 rainy season (about 20 - 80% above average). The heavy rains promoted vigorous vegetation growth in 2009, resulting in less bare ground capable of generating dust. Image credit: NOAA/Climate Prediction Center.

The Sahara and the Sahel: significant sources of dust
The summertime dust that affects Atlantic tropical storms originates over the southwestern Sahara (18° - 22° N) and the northwestern Sahel (15° - 18° N) (Figure 2). The dust that originates in the Southwest Sahara stays relatively constant from year to year. However, the dust from the northwestern Sahel varies significantly from year to year, and understanding this variation may be a key factor in improving our forecasts of seasonal hurricane activity in the Atlantic. The amount of dust that gets transported over the Atlantic depends on a mix of three main factors: the large scale and local scale weather patterns (windy weather transports more dust), how wet the current rainy season is (wet weather will wash out dust before it gets transported over the Atlantic), and how dry and drought-damaged the soil is. The level of drought experienced in the northwestern Sahel during the previous year's rainy season (June - October) is the key factor of the three in determining how much dust gets transported over the Atlantic during hurricane season, according to a January 2004 study published in Geophysical Research Letters published by C. Moulin and I. Chiapello. A dry rainy season the previous year will make an expanded area of loose soil which can create dust. It is also possible that the corresponding changes in vegetation can alter the regional weather patterns, causing more dust production.


Figure 2. Map of the mean summer dust optical thickness derived from satellite measurements between 1979 and 2000. Maximum dust amounts originate in the northern Sahel (15° to 18° N) and the Sahara (18° to 22° N). The Bodele depression in Chad is also an active dust source. Image credit: Evidence of the control of summer atmospheric transport of African dust over the Atlantic by Sahel sources from TOMS satellites (1979-2000) by C. Moulin and I. Chiapello, published in January 2004 in Geophysical Research Letters.

How dust suppresses hurricanes
Dust acts as a shield which keeps sunlight from reaching the surface. Thus, large amounts of dust can keep the sea surface temperatures up to 1°C cooler than average in the hurricane Main Development Region (MDR) off the coast of Africa, providing hurricanes with less energy to form and grow. Dust also affects the Saharan Air Layer (SAL), an layer of dry, dusty Saharan air that rides up over the low-level moist air over the tropical Atlantic. At the boundary between the SAL and low-level moist air where the trade winds blow is the trade wind inversion--a region of the atmosphere where the temperature increases with height. Since atmospheric temperature normally decreases with height, this "inversion" acts to but the brakes on any thunderstorms that try to punch through it. This happens because the air in a thunderstorm's updraft suddenly encounters a region where the updraft air is cooler and less buoyant than the surrounding air, and thus will not be able to keep moving upward. The dust in the SAL absorbs solar radiation, which heats the air in the trade wind inversion. This makes the inversion stronger, which inhibits the thunderstorms that power a hurricane. The dust may also act to interfere with the formation of cloud drops and rain drops that these thunderstorms need to grow, but little is known about such effects. It is possible that dust may act to help hurricanes by serving as "condensation nuclei"--centers around which raindrops can form and grow.

For additional reading
Dr. Evan published a study in Science magazine this March showing that 69% of the increase in Atlantic sea surface temperatures over the past 26 years could be attributed to decreases in the amount of dust in the atmosphere.

Jeff Masters

Hurricane

Updated: 6:26 PM GMT on August 19, 2011

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Fourth warmest May on record

By: JeffMasters, 10:01 PM GMT on June 16, 2009

The globe recorded its fourth warmest May on record, according to the National Climatic Data Center. The period January - May tied with 2003 as the sixth warmest such period on record. Global temperature records go back to 1880.

A warm and wet May for the U.S.
For the contiguous U.S., May temperatures were the 24th warmest in the 115-year record, according to the National Climatic Data Center. The Southeast region experienced its second wettest May in 115-years of record-keeping. In contrast, the West North Central region had their sixth driest May. Both Florida (9.86 inches) and Arkansas (10.91 inches) experienced their all-time wettest May. The last time Florida saw a record wet May was in 1976 when 9.15 inches of precipitation fell. Arkansas experienced its last record wet May in 1930 when 10.07 inches of precipitation fell. U.S. tornado activity was below average in May, according to NOAA's Storm Prediction Center.

On June 9, 2009, 14% of the contiguous United States was in moderate-to-exceptional drought. This is a drop from the 19% figure observed at the beginning of the year. The amount of the U.S. in the highest levels of drought, extreme to exceptional, decreased from 2.6% on May 12 to 1.5% on June 9. These extreme drought regions were in South Texas.

El Niño watch issued
NOAA's Climate Prediction Center issued an El Niño Watch last week, saying "that conditions are favorable for a transition from neutral to El Niño conditions during June - August 2009". The pattern of changes in surface winds, upper-level winds, sea surface temperatures, and deeper water heat content are all consistent with what has been observed during previous developing El Niños. We are currently experiencing neutral conditions, with ocean temperatures in the Equatorial Eastern Pacific just 0.2°C below the threshold for El Niño. In the week since the El Niño watch was issued, ocean temperatures have remained nearly steady in the Eastern Pacific, so we are not rushing into an El Niño just yet. As discussed in detail in an earlier blog post, most of our more advanced El Niño computer models are predicting a weak El Niño event for the coming Atlantic hurricane season. If this indeed occurs, it is likely that Atlantic hurricane activity will be suppressed due to the strong upper-level winds an El Niño usually brings to the tropical Atlantic, creating high wind shear that tears hurricanes apart.

Sea ice extent in the Arctic near average during May
May 2009 Northern Hemisphere sea ice extent was near average in May, coming in at 15th lowest (16th highest) since 1979, according to the National Snow and Ice Data Center. The record May low was set in 2004. The rate of ice decline in May accelerated, and by the end of the month the decline rate was equal to last year's rate. Warmer than usual temperatures over the Arctic during May contributed to this acceleration. The Arctic remains vulnerable to near-record melting this summer if much warmer than average temperatures occur over the region, since the ice is at record thinness this summer. Thin ice requires less energy to melt, and it also tends to be more fractured, with increased open water amid the ice. Since water absorbs more sunlight than ice, heat from the sun can more rapidly melt this fractured ice.

Jeff Masters

Climate Summaries

Updated: 10:24 PM GMT on October 21, 2011

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Atlantic hurricane outlook for the remainder of June

By: JeffMasters, 2:32 PM GMT on June 12, 2009

The last half of June is usually one of the quietest portions of hurricane season. In the 14 years since the current active hurricane period began in 1995, only four tropical storms formed in the last half of June. Thus, recent history gives us a 29% chance of a last-half-of-June named storm. None of those four storms since 1995 became a hurricane, and hurricanes are quite rare in June.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) have remained close to average over the tropical Atlantic between Africa and Central America this month (Figure 1). These are the are the coolest SST anomalies we've seen since 1994. The strength of the Azores-Bermuda high has been near average over the past two weeks, driving near-average trade winds. Stronger-than-average trade winds were observed through most of the period November 2008 - May 2009, which helped cool the tropical Atlantic substantially. Strong winds mix up colder water from the depths and cause greater evaporative cooling. The latest 2-week run of the GFS model predicts continued average trade winds over the tropical Atlantic for the remainder of June, so expect the near-average SSTs to continue over the tropical Atlantic as we head into July.

Typically, June tropical storms form over the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida, where water temperatures are warmest. SSTs are 26 - 28°C in these regions, which is about 0.5°C above average for this time of year. June storms typically form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance. African tropical waves, which serve as the instigators of about 85% of all major hurricanes, are usually too far south in June to trigger tropical storm formation. SSTs are too cold in June to allow storms to develop between the coast of Africa and the Lesser Antilles Islands--there has only been once such development in the historical record--Ana of 1979, which coincidentally will be the name given to this year's first storm.


Figure 1. Sea Surface Temperature (SST) departure from average for June 11, 2009. SSTs were near average over the tropical Atlantic. Note the large region of above average SSTs along the Equatorial Pacific off the coast of South America, signaling the possible start of an El Niño episode. Image credit: NOAA/NESDIS

El Niño
NOAA's Climate Prediction Center issued an El Niño Watch last week, saying "that conditions are favorable for a transition from neutral to El Niño conditions during June - August 2009". The pattern of changes in surface winds, upper-level winds, sea surface temperatures, and deeper water heat content are all consistent with what has been observed during previous developing El Niños. We are currently experiencing neutral conditions, with ocean temperatures in the Equatorial Eastern Pacific just 0.2°C below the threshold for El Niño. In the week since the El Niño watch was issued, ocean temperatures have remained nearly steady in the Eastern Pacific, so we are not rushing into an El Niño just yet. As I discussed in detail in an earlier post, most of our more advanced El Niño computer models are predicting a weak El Niño event for the coming Atlantic hurricane season. If this indeed occurs, it is likely that Atlantic hurricane activity will be suppressed due to the strong upper-level winds an El Niño usually brings to the tropical Atlantic, creating high wind shear that tears hurricanes apart.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart. The jet stream's band of strong high-altitude winds is the main source of wind shear in June over the Atlantic hurricane breeding grounds, since the jet is very active and located quite far south this time of year.

The jet stream over the past few weeks has been locked into a pattern where a southern branch (the subtropical jet stream) brings high wind shear over the Caribbean, and a northern branch (the polar jet stream) brings high wind shear offshore of New England. This often leaves a "hole" of low shear between the two branches off the coast of North Carolina, which is where Tropical Depression One formed at the end of May.

The jet stream is forecast (Figure 2) to maintain this two-branch pattern over the coming two weeks. This means that the waters offshore of the Carolinas are the most likely place for a tropical storm to form during this period.


Figure 2. Wind shear in m/s between 200 mb and 850 mb, as forecast by the 00Z June 12, 2009 run of the GFS model. The position of the subtropical jet stream is forecast to change little over the next two weeks, and this jet will bring high wind shear to the Caribbean and Gulf of Mexico for most of the remainder of June. There will at times be a region of low shear between the polar jet (northern set of arrows on the plots) and the subtropical jet, allowing for possible tropical development off the coast of North Carolina. Wind speeds are given in m/s; multiply by two to get a rough conversion to knots. Thus, the red regions of low shear range from 0 - 16 knots.

Steering currents
The steering current pattern over the past few weeks has not changed much, and is typical for June. We have an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. These troughs are frequent enough and strong enough to recurve any tropical storms or hurricanes that might penetrate north of the Caribbean Sea. Steering current patterns are predictable only about 3 - 5 days in the future, although we can make very general forecasts about the pattern as much as two weeks in advance. At present, it appears that the coming two weeks will maintain the typical June pattern, bringing many troughs of low pressure off the East Coast capable of recurving any June storms that might form. There is no telling what might happen during the peak months of August, September, and October--we might be in for a repeat of the favorable 2006 steering current pattern that recurved every storm out to sea--or the unfavorable 2008 pattern, that steered Ike and Gustav into the Gulf of Mexico.

Summary
Recent history suggests a 29% chance of a named storm occurring in the second half of June. Given that the current SST pattern and two-week wind shear forecast look fairly typical for June, I'll go with a 20% chance of a named storm forming during the last half of June. There's currently nothing out there of note, but we should start watching the region off the North Carolina coast 4 - 7 days from now.

Other stuff
Saturday, June 13 marks the last day of the Vortex2 tornado research project. The team of University of Michigan students writing our Vortex2 blog has posted some great photos and accounts of the storms they caught up to this week.

The Portlight.org charity is hard at work helping victims of the Volusia County, Florida floods.

Today's post will likely be my final "live" post until June 29, as I am headed to London, England, and Kefalonia Island, Greece for my first-ever European vacation. My fellow wunderground meteorologists will be posting to my blog if any tropical weather of note develops. I also recommend following the blog of wunderblogger Weather456, who works as a forecaster on St. Kitts Island in the Lesser Antilles. If the tropics remain quiet, I've prepared some "canned" blogs that will be posted on my blog. The topics include:

--The Atlantic Meridional Mode: implications for the 2009 hurricane season
--African dust forecast for the 2009 Atlantic hurricane season
--U.S. vulnerability to sea level rise: the Coastal Vulnerability Index (CVI)
--The six Hurricane and Typhoon Hunter flights that never came back
--Sea level rise: the forecast
--Sea level rise in the Northeast U.S. from ocean current changes

Jeff Masters

Hurricane

Updated: 6:26 PM GMT on August 19, 2011

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Sea level rise: what has happened so far

By: JeffMasters, 2:05 PM GMT on June 10, 2009

Sea level has been rising globally since the late 1700s. This rise has accelerated in recent decades, thanks to increased melting of glaciers and ice sheets due to a warmer climate, plus the fact that warmer oceans are less dense and expand, further increasing sea level. Though sea level rise appears to have slowed over the past five years, it will significantly accelerate if the climate warms the 2 - 3°C it is expected to this century. If these forecasts of a warmer world prove accurate, higher sea levels will be a formidable challenge for millions of people world-wide during the last half of this century. Sea level rise represents one of my personal top two climate change concerns (drought is the other). I'll present a series of blog posts over the coming months focusing on at-risk areas in the U.S., Caribbean, and world-wide. Today, I focus on the observed sea level rise since the Ice Age.

What's at stake
Higher sea levels mean increased storm surge inundation, coastal erosion, loss of low-lying land areas, and salt water contamination of underground drinking water supplies. About 44% of the Earth's 6.7 billion people live within 150 km (93 miles) of the coast, and 600 million people live at an elevation less than ten meters (33 feet). Eight of the ten largest cities in the world are sited on the ocean coast. In the U.S., the coastal population has doubled over the past 50 years. Fourteen of the twenty largest urban centers are located within 100 km of the coast, and are less than ten meters above sea level (McGranahan et al., 2007). The population of many vulnerable coastal regions are expected to double by 2050, according to the U.S. Census Bureau.

Sea level rise since the Ice Age
Before the most recent Ice Age, sea level was about 4 - 6 meters (13 - 20 feet) higher than at present. Then, during the Ice Age, sea level dropped 120 meters (395 ft) as water evaporated from the oceans precipitated out onto the great land-based ice sheets. The former ocean water remained frozen in those ice sheets during the Ice Age, but began being released 12,000 - 15,000 years ago as the Ice Age ended and the climate warmed. Sea level increased about 115 meters over a several thousand year period, rising 40 mm/year (1.6"/yr) during one 500-year pulse of melting 14,600 years ago. The rate of sea level rise slowed to 11 mm/year (0.43"/yr) during the period 7,000 - 14,000 years ago (Bard et al., 1996), then further slowed to 0.5 mm/yr 6,000 - 3,000 years ago. About 2,000 - 3,000 years ago, the sea level stopped rising, and remained fairly steady until the late 1700s (IPCC 2007). One exception to this occurred during the Medieval Warm Period of 1100 - 1200 A.D., when warm conditions similar to today's climate caused the sea level to rise 5 - 8" (12 - 21 cm) higher than present (Grinsted et al., 2008). This was probably the highest the sea has been since the beginning of the Ice Age, 110,000 years ago. There is a fair bit of uncertainty in all these estimates, since we don't have direct measurements of the sea level.


Figure 1. Global sea level from 200 A.D. to 2000, as reconstructed from proxy records of sea level by Moberg et al. 2005. The thick black line is reconstructed sea level using tide gauges (Jevrejeva, 2006). The lightest gray shading shows the 5 - 95% uncertainty in the estimates, and the medium gray shading denotes the one standard deviation error estimate. The highest global sea level of the past 110,000 years likely occurred during the Medieval Warm Period of 1100 - 1200 A.D., when warm conditions similar to today's climate caused the sea level to rise 5 - 8" (12 - 21 cm) higher than present. Image credit: Grinsted, A., J.C. Moore, and S. Jevrejeva, 2009, "Reconstructing sea level from paleo and projected temperatures 200 to 2100 AD", Climate Dynamics, DOI 10.1007/s00382-008-0507-2, 06 January 2009.

Sea level rise over the past 300 years
Direct measurements of sea level using tide gauges began in Amsterdam in 1700. Additional tide gauges began recording data in Liverpool, England in 1768 and in Stockholm, Sweden in 1774. These gauges suggest that a steady acceleration of sea rise of 0.01 mm per year squared began in the late 1700s, resulting in a rise in sea level of 2.4" (6 cm, 0.6 mm/yr) during the 19th century and 7.5" (19 cm, 1.9 mm/yr) during the 20th century (Jevrejeva et al., 2008). There is considerable uncertainty in just how much sea level rise has occurred over the past few centuries, though. Measuring global average sea level rise is a very tricky business. For starters, one must account for the tides, which depend on the positions of the Earth and Moon on a cycle that repeats itself once every 18.6 years. Tide gauges are scattered, with varying lengths of record. The data must be corrected since land is sinking in some regions, due to pumping of ground water, oil and gas extraction, and natural compaction of sediments. Also, the land is rising in other regions, such as Northern Europe, where it is rebounding from the lost weight of the melted glaciers that covered the region during the last Ice Age. Ocean currents, precipitation, and evaporation can cause a 20 inch (50 cm) difference in sea level in different portions of the ocean. As a result of all this uncertainty, the 1996 Intergovernmental Panel on Climate Change (IPCC) report gave a range of 4 - 10" (10 - 25 cm) for the observed sea level rise of the 20th century. The 2007 IPCC report narrowed this range a bit, to 5 - 9" (12 - 22 cm), or 1.2 - 2.2 mm/year. Rates of sea level rise are much higher in many regions. In the U.S., the highest rates of sea-level rise are along the Mississippi Delta region--over 10 mm/yr, or 1 inch/2.5 years (USGS, 2006). This large relative rise is due, in large part, to the fact that the land is sinking.


Figure 2. Absolute sea level rise between 1955 and 2003 as computed from tide gauges and satellite imagery data. The data has been corrected for the rising or sinking of land due to crustal motions or subsidence of the land, so the relative sea level rise along the coast will be different than this. The total rise (in inches) for the 48-year period is given in the top scale, and the rate in mm/year is given in the bottom scale. The regional sea level variations shown here resulted not only from the input of additional water from melting of glaciers and ice caps, but also from changes in ocean temperature and density, as well as changes in precipitation, ocean currents, and river discharge. Image credit: IPCC, 2007

Sea level rise over the past 15 years
According to the Intergovernmental Panel on Climate Change (IPCC) 2007 report, sea level accelerated from the 1.2 - 2.2 mm/yr observed during the 20th century to 3.1 mm/year during the period 1993 - 2003. These estimates come from high resolution measurements from satellite radar altimeters, which began in 1992. Tide gauges showed a similar level of sea level rise during that ten-year period. The IPCC attributed more than half of this rise (1.6 mm/yr) to the fact that the ocean expanded in size due to increased temperatures. Another 1.2 mm/yr rise came from melting of Greenland, West Antarctica, and other land-based ice, and about 10% of the rise was unaccounted for. However, during the period 2003 - 2008, sea level rise slowed to 2.5 mm/year, according to measurements of Earth's gravity from the GRACE satellites (Cazenave et al., 2008). This reduction in sea level rise probably occurred because ocean sea surface temperatures have not warmed since 2003 (Figure 3). The authors concluded that sea level rise due to ocean warming decreased more than a factor of five from 2003 - 2008, compared to 1993 - 2003, contributing only 0.3 mm/yr vs. the 1.6 mm/yr previously.


Figure 3. Global average sea surface temperatures (SSTs) from 1990-2008. SSTs have not increased in the past seven years. Image credit: NASA/GISS.

For more information
The best source of information I found while compiling my sea level pages was the Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region report by the U.S. Climate Science Program. It has a huge number of references to all the latest science being done on sea level rise.

References
Bard, E., et al., 1996, "Sea level record from Tahiti corals and the timing of deglacial meltwater discharge", Nature 382, pp241-244, doi:10.1038/382241a0.

Cazenave et al., 2008, "Sea level budget over 2003-2008: A reevaluation from satellite altimetry and Argo", Global and Planetary Change, 2008; DOI:10.1016/j.gloplacha.2008.10.004

Grinsted, A., J.C. Moore, and S. Jevrejeva, 2009, "Reconstructing sea level from paleo and projected temperatures 200 to 2100 AD", Climate Dynamics, DOI 10.1007/s00382-008-0507-2, 06 January 2009.

IPCC (Intergovernmental Panel on Climate Change), 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, UK, and New York, 996 pp.

Jevrejeva, S., J.C. Moore, A. Grinsted,, and P.L. Woodworth, 2008, "Recent global sea level acceleration started over 200 years ago?", Geophysical Research Letters, 35, L08715, doi:10.1029/2008GL033611, 2008.

McGranahan, G., D. Balk, and B. Anderson, 2007, "The rising tide: assessing the risks of climate change and human settlements in low elevation coastal zones", Environment & Urbanization, 19(1), 17-37.

Moberg, A., et al., 2005, "Highly variable northern hemisphere temperature reconstructed from low- and high-resolution proxy data", Nature 433, pp613-617, doi:10.1038/nature03265.

United States Geological Survey (USGS), 2006, National Assessment of Coastal Vulnerability to Sea-Level Rise: Preliminary Results for the U.S. Gulf of Mexico Coast, U.S. Geological Survey Open-File Report 00-179.

Tropical update
The tropical Atlantic is quiet, and the only region worth watching is the Western Caribbean, which could see formation of a tropical disturbance with heavy thunderstorm activity this weekend.

Jeff Masters

Climate Change Sea level rise

Updated: 7:45 PM GMT on August 16, 2011

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Vortex2 tornado study finally gets some twisters to study

By: JeffMasters, 1:56 PM GMT on June 08, 2009

A proven way to reduce the incidence of dangerous weather phenomena is to schedule a multi-million dollar field experiment to study the phenomena. Up until this past weekend, that has certainly been true of this year's $10 million Vortex2 tornado study. The 7-week study (which also runs next year) has deployed an armada of over 100 storm chasing vehicles across the Great Plains this Spring, but has largely been frustrated by an exceptionally quiet tornado season. Tornado activity in May was less than half of what was observed last year in May, thanks to a ridge of high pressure that has dominated the weather. The residents of Tornado Alley ran out of luck over the weekend, though, as a strong low pressure system and associated cold front brought severe weather and multiple tornadoes to the region. Sixteen tornado reports were received by NOAA's Storm Prediction Center yesterday, and three on Friday. The team of University of Michigan students that has been writing our featured Vortex2 blog caught some excellent pictures of tornadoes on both Friday and Sunday. Yesterday was probably the last best chance for the Vortex2 project to document a strong tornado, since the project ends this Saturday and no significant tornado outbreaks appear likely for the remainder of this week.

Aurora, Colorado tornado yesterday
A tornado with a 3/4 mile wide debris cloud swept through Aurora, Colorado yesterday, staying on the ground for 8 - 11 miles and damaging a shopping mall, but causing no deaths or injuries. The tornado passed close to one of the high-resolution Terminal Doppler Weather Radars (TDWRs) that we now feature on our web site (see the radar FAQ for more details on these great new additions to our radar offerings). Posted below are the reflectivity and Doppler velocity images from the tornado, showing the amazing fine-scale details these high-resolution radars offer.



Figure 1. Radar reflectivity (top) and Doppler velocity (bottom) from the Denver, Colorado Terminal Doppler Weather Radar (TDWR), which caught the classic signature of a supercell thunderstorm tornado over Aurora, Colorado. A tornado dropped down from the low-level mesocyclone inside the parent supercell thunderstorm at the time of these images. Yellow colors located right next to greens/blues indicate that winds are moving towards and away from the radar in close proximity, the signature of strong rotation at low levels. Also visible on the plot are the winds spreading out from a downdraft on the rear side of the tornado. Black arrows denote the direction of wind flow. The dryline was bent back into a E-W orientation near Denver, creating an area of moisture convergence, which triggered thunderstorm formation.

Western Caribbean disturbance unlikely to develop this week
As area of disturbed weather over the Western Caribbean has brought rains of 2 - 3 inches over portions of Nicaragua and Honduras over the past few days. Wind shear is a high 20 - 30 knots over the disturbance, and no computer models are indicating that the disturbance will develop this week.

Jeff Masters, with help from wunderground's tornado expert, Dr. Rob Carver

Tornado

Updated: 8:42 PM GMT on October 24, 2011

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Western Caribbean disturbance unlikely to develop this week

By: JeffMasters, 4:57 PM GMT on June 07, 2009

An area of disturbed weather is bringing some heavy rains to Nicaragua and Honduras and the adjacent waters of the Western Caribbean. This disturbance has generated 2 - 3 inches of rain over these countries over the past two days, and is likely to bring an additional 2 - 3 inches of rain to northeastern Honduras and Nicaragua over the next two days. The disturbance is expected to gradually drift northwards, bringing heavy rain to the Cayman Islands, Jamaica, and Cuba by Monday or Tuesday. The disturbance is under prohibitively high wind shear of 30 - 40 knots, and is not a threat to develop today or Monday. Some of the computer models are predicting wind shear may fall low enough to allow development of this system 4 - 7 days from now, but the models have been rather inconsistent in the location and timing of any such development. For now, the chances of a tropical depression forming from this disturbance within the next week appear low, less than 30%.


Figure 1. Visible satellite image of the Western Caribbean disturbance.

I'll have an update Monday.

Jeff Masters

Hurricane

Updated: 7:58 PM GMT on June 08, 2009

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El Niño Watch issued by NOAA; Western Caribbean development next week?

By: JeffMasters, 1:55 PM GMT on June 05, 2009

NOAA's Climate Prediction Center issued an El Niño Watch yesterday, saying "that conditions are favorable for a transition from neutral to El Niño conditions during June - August 2009". The pattern of changes in surface winds, upper-level winds, sea surface temperatures, and deeper water heat content are all consistent with what has been observed during previous developing El Niños. As I discussed in detail in last Friday's post, most of our more advanced El Niño computer models are predicting a weak El Niño event for the coming Atlantic hurricane season. If this indeed occurs, it is likely that Atlantic hurricane activity will be suppressed due to the strong upper-level winds an El Niño usually brings to the tropical Atlantic, creating high wind shear that tears hurricanes apart.


Figure 1. Departure from average of the heat content of the upper 300 meters of the ocean in the Equatorial Eastern Pacific. Much of this increase in heat content is due to a large area of waters 2 - 4°C warmer than average at the thermocline (a depth of 50 - 150 meters). The heat content of the ocean has been steadily increasing since January, consistent with a developing El Niño episode. Image credit: NOAA's Climate Prediciton Center.

Western Caribbean development possible next week
An area of disturbed weather has developed over Central America and the adjacent waters of the Eastern Pacific and Western Caribbean, associated with a tropical wave interacting with the Intertropical Convergence Zone (ITCZ) in the Eastern Pacific. This disturbance has generated 1 - 2 inches of rain over Costa Rica and western Panama over the past day, and is likely to bring 4 - 6 more inches of rain to those areas and Nicaragua over the next 3 - 4 days, as the storm drifts northwards into the Western Caribbean. The subtropical jet stream, which is currently bringing high wind shear to the Caribbean, is expected to shift northwards next week, bringing low wind shear to the region. The last few runs of several of our major dynamical computer weather forecast models have been pointing to the possible development of a tropical depression southwest of Jamaica by Thursday of next week. Heavy rains from the disturbance should spread into Jamaica and Cuba by Thursday and Friday, and may affect the Bahamas, Haiti, and South Florida 7 - 8 days from now.


Figure 2. Visible satellite image of the Central American disturbance expected to cross over into the Western Caribbean next week.

I'll have an update this weekend, probably on Sunday.

Jeff Masters

Hurricane

Updated: 6:26 PM GMT on August 19, 2011

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Average hurricane season foreseen by TSR

By: JeffMasters, 1:33 PM GMT on June 04, 2009

The ballots are all in now, and all three major seasonal forecasting groups are calling for a near-average Atlantic hurricane season in 2009--the British private forecasting firm Tropical Storm Risk, Inc. (TSR) has joined the ranks of NOAA and Colorado State University in calling for near-average activity. The latest TSR forecast issued today calls for 10.9 named storms, 5.2 hurricanes, 2.2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 72% of average. The storm numbers are close to the 50-year average of 10 named storms, 6 hurricanes, and 2 intense hurricanes, and are sharp reduction from their April forecast of 15 named storms, 7.8 hurricanes, and 3.6 intense hurricanes. TSR predicts a 50% chance that this season will be in the bottom 1/3 of years historically, and a 40% chance that U.S. landfalling activity will be in the lowest 1/3 of years historically. TSR gives a 32% chance of a near-normal season, and a 17% chance of a below normal season. TSR rates their skill level as 26% above chance at forecasting the number of named storms, 15% skill for hurricanes, and 19% skill for intense hurricanes.

TSR projects that 3.2 named storms will hit the U.S., with 1.3 of these being hurricanes. The averages from the 1950-2008 climatology are 3.2 named storms and 1.5 hurricanes. Their skill in making these April forecasts for U.S. landfalls is 7 - 18% above chance. In the Lesser Antilles Islands of the Caribbean, TSR projects 0.9 named storms, 0.4 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites two main factors for their reduced forecast: a large and unexpected cooling of sea surface temperatures in the tropical Atlantic, and warmer SSTs in the Equatorial Eastern Pacific (which might lead to an El Niño event that will bring high wind shear to the Atlantic). TSR expects faster than than normal trade winds from July - September over the Main Development Region (MDR) for hurricanes over the Atlantic (the region between 10° - 20° N from Central America to Africa, including all of the Caribbean). Trade winds are forecast to be 0.83 meters per second (about 1.7 mph) faster than average in this region, which would create less spin for developing storms, and allow the oceans to cool down, due to increased mixing of cold water from the depths and enhanced evaporational cooling. TSR forecasts that SSTs will cool an additional 0.3°C compared to average over the MDR during hurricane season.

Portlight.org offering relief to Florida flood victims
Tropical disturbance 90L dropped as much as two feet of rain over Northeastern Florida in May, causing severe flooding. In Volusia County, at least 1500 homes were damaged by the flooding, and many of these were in low-income housing projects where the residents did not have flood insurance. Portlight Strategies, Inc., is now working to assist in this area by providing durable medical equipment to the disabled, elderly, or injured that have lost equipment due to the flooding. Specifically, the Portlight team will be assisting with the rebuilding of two homes. One of the homes is owned by a single mother who stood in her house crying, in two feet of water, as she prepared to go to her daughters graduation. The other home is owned by a elderly woman whose husband passed away two years ago. Neither of these families had flood insurance, and can not afford even the lowest interest rate loans provided by FEMA. Portlight's work in Holly Hill, FL will begin on Friday June 12; if you are interested in volunteering, please contact John Wilbanks, john@portlight.org 843-200-6022. There are plenty of stories very similar to these two. Portlight's ability to help is only limited by your assistance, so please consider volunteering or donating today by visiting the Portlight disaster relief blog..


Figure 1. Rainfall amounts over Florida for the two weeks ending on May 27, 2009. Image credit: NOAA.

Hurricane

Updated: 6:26 PM GMT on August 19, 2011

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Average hurricane season foreseen by CSU, NOAA, and TSR

By: JeffMasters, 4:45 PM GMT on June 02, 2009

A near-average Atlantic hurricane season is on tap for 2009, according to the seasonal hurricane forecast issued June 2 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 11 named storms, 5 hurricanes, and 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 88% of average. Between 1950 - 2000, the average season had 10 named storms, 6 hurricanes, and 2 intense hurricanes. But since 1995, the beginning of an active hurricane period in the Atlantic, we've averaged 15 named storms, 8 hurricanes, and 4 intense hurricanes per year. The new forecast is a step down from their April forecast, which called for 12 named storms, 6 hurricanes, and 2 intense hurricanes. The new forecast calls for a near-average chance of a major hurricane hitting the U.S., both along the East Coast (28% chance, 31% chance is average) and the Gulf Coast (28% chance, 30% chance is average). The Caribbean is also forecast to have an average risk of a major hurricane.

The forecasters cited several reasons for an average season:

1) Sea surface temperature (SST) anomalies in the tropical Atlantic are quite cool. In fact, these SST anomalies are at their coolest level since July 1994. Cooler-than-normal waters provide less heat energy for developing hurricanes. In addition, an anomalously cool tropical Atlantic is typically associated with higher sea level pressure values and stronger-than-normal trade winds, indicating a more stable atmosphere with increased levels of vertical wind shear detrimental for hurricanes. Substantial cooling began in November 2008 (Figure 1), primarily due to a stronger than average Bermuda-Azores High that drove strong trade winds. These strong winds increased the mixing of cool waters to the surface from below, and caused increased evaporational cooling.

2) Hurricane activity in the Atlantic is lowest during El Niño years and highest during La Niña or neutral years. This occurs because El Niño conditions bring higher wind shear over the tropical Atlantic. The CSU team expects the current neutral conditions may transition to El Niño conditions (70% chance) by this year's hurricane season. I discussed the possibility of a El Niño conditions developing this year in a blog posted Friday.


Figure 1. Change in Sea Surface Temperature anomaly between November 2008 and 2009. Most of the Atlantic has cooled significantly, relative to normal, over the past 7 months. Image credit: NOAA/ESRL.

Analogue years
The CSU team picked five previous years when atmospheric and oceanic conditions were similar to what we are seeing this year: neutral to slightly warm ENSO conditions, slightly below-average tropical Atlantic SSTs, and above-average far North Atlantic SSTs during April-May. Those five years were 2002, which featured Hurricane Lili that hit Louisiana as a Category 1 storm; 2001, featuring Category 4 storms Michelle, which hit Cuba, and Iris, which hit Belize; 1965, which had Category 3 Betsy that hit New Orleans; 1960, which had two Category 5 hurricanes, Ethyl and Donna; and 1959, which had Category 3 Hurricane Gracie, which hit South Carolina. The mean activity for these five years was 10 named storms, 6 hurricanes, and 2 intense hurricanes, almost the same as the 2009 CSU forecast.

How accurate are the June forecasts?
The June forecasts by the CSU team have historically offered a skill of 20 - 30% higher than a "no-skill" forecast using climatology (Figure 2). This is a decent amount of skill for a seasonal forecast, and these June forecasts can be useful to businesses such as the insurance industry and oil and gas industry that need to make bets on how active the coming hurricane season will be. This year's June forecast uses the same formula as last year's June forecast, which did quite well predicting the 2008 hurricane season (prediction: 15 named storms, 8 hurricanes, 4 intense hurricanes; observed: 16 named storms, 8 hurricanes, 5 intense hurricanes). An Excel spreadsheet of their forecast skill (expressed as a mathematical correlation coefficient) show values from 0.44 to 0.58 for their June forecasts, which is respectable.


Figure 2. Accuracy of long-range forecasts of Atlantic hurricane season activity performed at Colorado State University (CSU) by Dr. Bill Gray's team (colored squares) and Tropical Storm Risk, Inc. (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.

NOAA's 2009 hurricane season forecast
The National Oceanic and Atmospheric Administration (NOAA), issued its 2009 Atlantic hurricane season forecast on May 21. NOAA anticipates that an average season it most likely, giving a 50% chance of a near-normal season, 25% chance of an above-normal season, and a 25% chance of a below-normal season. They give a 70% chance that there will be 9 - 14 named storms, 4 - 7 hurricanes, 1 - 3 major hurricanes, and an Accumulated Cyclone Energy (ACE) in the 65% - 130% of normal range. The forecasters cited the following main factors that will influence the coming season:

1) We are in an active period of hurricane activity that began in 1995, thanks to a natural decades-long cycle in hurricane activity called the Atlantic Multidecadal Oscillation (AMO).

2) There will either be an El Niño event or neutral conditions in the Equatorial Eastern Pacific. An El Niño event should act to reduce Atlantic hurricane activity. However, our skill at predicting an Niño in late May/early June is poor, so there is high uncertainty about how active the coming hurricane season will be.

3) Cooler-than-average SSTs are currently present in the eastern tropical Atlantic. These cool SSTs are forecast to persist through into August-September-October (ASO). ASO SSTs in the eastern tropical Atlantic have not been below average since 1997. Cooler SSTs in that region are typically associated with a reduction in Atlantic hurricane activity.

Thus, they expect that even though we are in an active hurricane period, the presence of an El Niño or cool SSTs in the eastern Atlantic could easily suppress activity, making a near-average season the most likely possibility. They note that two promising computer models, the NOAA CFS model and the European Center for Medium-Range Weather Forecasts (ECMWF) Global Climate Model System 3, both forecast the possibility of a below-average hurricane season.

2009 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR) has joined the ranks of NOAA and Colorado State University in calling for near-average activity. The latest TSR forecast issued June 4 calls for 10.9 named storms, 5.2 hurricanes, 2.2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 72% of average. The storm numbers are close to the 50-year average of 10 named storms, 6 hurricanes, and 2 intense hurricanes, and are sharp reduction from their April forecast of 15 named storms, 7.8 hurricanes, and 3.6 intense hurricanes. TSR predicts a 50% chance that this season will be in the bottom 1/3 of years historically, and a 40% chance that U.S. landfalling activity will be in the lowest 1/3 of years historically. TSR gives a 32% chance of a near-normal season, and a 17% chance of a below normal season. TSR rates their skill level as 26% above chance at forecasting the number of named storms, 15% skill for hurricanes, and 19% skill for intense hurricanes.

TSR projects that 3.2 named storms will hit the U.S., with 1.3 of these being hurricanes. The averages from the 1950-2008 climatology are 3.2 named storms and 1.5 hurricanes. Their skill in making these April forecasts for U.S. landfalls is 7 - 18% above chance. In the Lesser Antilles Islands of the Caribbean, TSR projects 0.9 named storms, 0.4 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites two main factors for their reduced forecast: a large and unexpected cooling of sea surface temperatures in the tropical Atlantic, and warmer SSTs in the Equatorial Eastern Pacific (which might lead to an El Niño event that will bring high wind shear to the Atlantic). TSR expects faster than than normal trade winds from July - September over the Main Development Region (MDR) for hurricanes over the Atlantic (the region between 10° - 20° N from Central America to Africa, including all of the Caribbean). Trade winds are forecast to be 0.83 meters per second (about 1.7 mph) faster than average in this region, which would create less spin for developing storms, and allow the oceans to cool down, due to increased mixing of cold water from the depths and enhanced evaporational cooling. TSR forecasts that SSTs will cool an additional 0.3°C compared to average over the MDR during hurricane season.

Air France crash
The Air France Flight 447 A330 aircraft that disappeared over the mid-Atlantic Ocean yesterday definitely crossed through a thunderstorm complex near the Equator, according to a detailed meteorological analysis by Tim Vasquez. He concludes that "the A330 would have been flying through significant turbulence and thunderstorm activity for about 75 miles (125 km), lasting about 12 minutes of flight time" but that "complexes identical to this one have probably been crossed hundreds of times over the years by other flights without serious incident". See also the excellent CIMSS satellite blog for more images and analysis of the weather during the flight.

Invest 92
NHC is tracking a storm near the Azores Islands (Invest 92L) that is probably the remnants of the core of an extratropical cyclone that closed off some warm air at the center. The system has developed some heavy thunderstorm activity near its center, making this a hybrid storm. However, with ocean temperatures near 62°F (16°C), this storm has little chance of becoming a named subtropical storm.

Jeff Masters

Hurricane

Updated: 6:27 PM GMT on August 19, 2011

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Hurricane season begins today; normal June activity expected

By: JeffMasters, 1:38 PM GMT on June 01, 2009

Hurricane season is upon us, and it's time to take a look at the prevailing conditions and 2-week forecast for tropical cyclone activity in the Atlantic. June is typically the quietest month of the Atlantic hurricane season. On average, we see only one named storm every two years in June. Only one major hurricane has made landfall in June--Category 4 Hurricane Audrey of 1957, which struck the Texas/Louisiana border area on June 27 of that year, killing 550. The highest number of named storms for the month is three, which occurred in 1936 and 1968. In the fourteen years since the current active hurricane period began in 1995, there have been eleven June named storms (if we include last year's Tropical Storm Arthur, which really formed on May 31). Five tropical storms have formed in the first half of June in that 14-year period, giving a historical 36% chance of a first-half-of-June named storm.


Figure 1. Tracks of all June tropical storms and hurricanes, 1851 - 2007.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) are close to average over the tropical Atlantic between Africa and Central America this year (Figure 2). These temperatures are some of the coolest we've seen since 1995, when the current active hurricane period began. This year's cool SSTs should prevent a repeat of the unforgettable Hurricane Season of 2005, which had the highest SSTs on record in the tropical Atlantic. Note also that SSTs along the Equatorial Pacific off the coast of South America are quite a bit above average, signaling the possible start of an El Niño episode. As I discussed in Friday's post, odds are increasing for a weak El Niño to form in time for hurricane season, and this should cut down on the number and intensity of Atlantic tropical storms and hurricanes this year. However, if an El Niño is developing, it shouldn't start affecting Atlantic hurricane activity until August.

Typically, June storms only form over the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida, where water temperatures are warmest. SSTs are 26 - 28°C in these regions, which is about 0.5°C above average for this time of year. June storms typically form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance. African tropical waves, which serve as the instigators of about 85% of all major hurricanes, are usually too far south in June to trigger tropical storm formation. Every so often, a tropical wave coming off the coast of Africa moves far enough north to act as a seed for a June tropical storm. This was the case for Arthur of 2008 (which also had major help from the spinning remnants of the Eastern Pacific's Tropical Storm Alma). Another way to get Atlantic June storms is for a disturbed weather area in the Eastern Pacific Intertropical Convergence Zone (ITCZ) to push north into the Western Caribbean and spawn a storm there. This was the case for Tropical Storm Alberto of 2006 (which may have also had help from an African wave). SSTs are too cold in June to allow storms to develop between the coast of Africa and the Lesser Antilles Islands--there has only been once such development in the historical record--Ana of 1979, which coincidentally will be the name given to this year's first storm.


Figure 2. Sea Surface Temperature (SST) departure from average for June 1, 2009. SSTs were near average over the tropical Atlantic. Note the large region of above average SSTs along the Equatorial Pacific off the coast of South America, signaling the possible start of an El Niño episode. Image credit: NOAA/NESDIS.

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 3) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. As we can see, the heat energy available in the tropical Atlantic has declined considerably since 2005, when the highest SSTs ever measured in the tropical Atlantic occurred. TCHP this year is similar to last year's levels, which were high enough to support five major hurricanes.


Figure 3. Tropical Cyclone Heat Potential (TCHP) for May 31 2005 (top), May 31 of last year (middle) and May 30 2009 (bottom). TCHP is a measure of the total heat energy available in the ocean. Record high values of TCHP were observed in 2005. TCHP this year is much lower, and similar to last year. Image credit: NOAA/AOML.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart. The jet stream's band of strong high-altitude winds is the main source of wind shear in June over the Atlantic hurricane breeding grounds, since the jet is very active and located quite far south this time of year.

The jet stream over the past few weeks has been locked into a pattern where a southern branch (the subtropical jet stream) brings high wind shear over the Caribbean, and a northern branch (the polar jet stream) brings high wind shear offshore of New England. This leaves a "hole" of low shear between the two branches off the coast of North Carolina, which is where Tropical Depression One formed. The low shear "hole" has dipped down into the northern Gulf of Mexico a few times. Disturbance 90L, which almost developed into a tropical storm before it came ashore in Mississippi/Alabama on May 23, took advantage of one of these low-shear areas.

The jet stream is forecast to maintain this two-branch pattern over the coming ten days. This means that the waters offshore of the Carolinas are the most likely place for a tropical storm to form during this period, though the northern Gulf of Mexico will at times have shear low enough to allow tropical storm formation. The latest 16-day forecast by the GFS model (Figure 4) predicts that the subtropical jet will weaken and retreat northwards by the middle of June, creating low-shear conditions over the Caribbean. This is a typical occurrence for mid-June, and we need to start watching the Western Caribbean for tropical storm formation by the middle of the month.


Figure 4. Wind shear forecast from the 00Z GMT June 1, 2009 run of the GFS model for June 1 (left panel) and June 17 (right panel). Currently, the polar jet stream is bringing high wind shear to the waters offshore New England, and the subtropical jet is bringing high wind shear to the Caribbean. This leaves the waters off the coast of North Carolina under low shear, making this area the most favored region for tropical storm formation over the next 7 - 10 days. By June 17, the subtropical jet is expected to weaken and move northwards, leaving the Caribbean under low shear, and favoring that region for tropical storm formation. Wind speeds are given in m/s; multiply by two to get a rough conversion to knots. Thus, the red regions of low shear range from 0 - 16 knots.

Dry air and African dust
It's too early to concern ourselves with dry air and dust coming off the coast of Africa, since these dust outbreaks don't make it all the way to the June tropical cyclone breeding grounds in the Western Caribbean and the Gulf of Mexico. Developing storms do have to contend with dry air from Canada moving off the U.S. coast; this was a key reason why 2007's Subtropical Storm Andrea never became a tropical storm. Dr. Amato Evan of the University of Wisconsin will issue his dust forecast for the coming hurricane season later this week, and I'll be discussing his forecast in an upcoming post.

Steering currents
The steering current pattern over the past few weeks has been typical for June, with an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. These troughs are frequent enough and strong enough to recurve any tropical storms or hurricanes that might penetrate north of the Caribbean Sea. Steering current patterns are predictable only about 3-5 days in the future, although we can make very general forecasts about the pattern as much as two weeks in advance. At present, it appears that the coming two weeks will maintain the typical June pattern, bringing many troughs of low pressure off the East Coast capable of recurving any June storms that might form. There is no telling what might happen during the peak months of August, September, and October--we might be in for a repeat of the favorable 2006 steering current pattern that recurved every storm out to sea--or the unfavorable 2008 pattern, that steered Ike and Gustav into the Gulf of Mexico.

Summary
Recent history suggests a 36% chance of a named storm occurring in the first half of June. The current conditions in the atmosphere and ocean are near average, so expect about a 1/3 chance of a named storm between now and June 15. The computer models are currently not forecasting development of any tropical storms over the next seven days.

I'll have an update Tuesday afternoon, when I'll discuss the Colorado State University June Atlantic Hurricane season forecast by Dr. Phil Klotzbach and Dr. Bill Gray, which will be issued Tuesday morning.

My next analysis and 2-week outlook for hurricane season is scheduled for June 13.

Jeff Masters

Hurricane

Updated: 6:27 PM GMT on August 19, 2011

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.