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Hurricane Season 2011: Tropical Storm Gert (Atlantic Ocean)
08.17.11
 
On August 16, 2011 at 0005 UTC, TRMM noticed a small area of heavy rainfall in Tropical Storm Gert. › View larger image
On August 16, 2011 at 0005 UTC, TRMM noticed a small area of heavy rainfall (red), falling at about 2 inches (50 mm) per hour in Tropical Storm Gert's northeastern quadrant. Yellow and green areas indicate moderate rainfall between .78 to 1.57 inches (20 to 40 mm) per hour.
Credit: NASA/SSAI, Hal Pierce
NASA's TRMM Satellite Sees Last Burst of Energy in Tropical Storm Gert

Rainfall is an indicator of strength of a tropical cyclone, and NASA's Tropical Rainfall Measuring Mission or TRMM satellite captured what appeared to be one last burst of heavy rainfall in Gert yesterday.

TRMM passed over Gert on August 16 at 0005 UTC and noticed a few powerful thunderstorms and an area of heavy rainfall in its northeastern quadrant.

By 2100 UTC (5 p.m. EDT) on August 16, Gert had stopped qualifying as a tropical cyclone and was labelled a post-tropical cyclone. At that time it was about 505 miles south of Cape Race, Newfoundland, Canada near 39.5 North and 54.7 West. It was racing through the Northern Atlantic in a northeasterly direction at 26 knots and speeding into the the North Atlantic's hurricane history book.

Text Credit: Rob Gutro, NASA Goddard Space Flight Center, Greenbelt, Md.





August 16, 2011

AIRS infrared image of Gert taken on August 15 at 05:41 UTC (1:41 a.m. EDT). › View larger image
This infrared image from the AIRS instrument on NASA's Aqua satellite was taken on Aug. 15 at 05:41 UTC (1:41 a.m. EDT). At this time, Gert had a small concentration of strong thunderstorms (purple) around the center of circulation. The blue color indicates less cold cloud top temperatures.
Credit: NASA/JPL, Ed Olsen
Tropical Storm Gert's Warming Cloud Tops Spell Trouble

Cloud top temperatures are observed by infrared instruments that fly aboard satellites, and NASA's Aqua satellite revealed that temperatures in Tropical Storm Gert have warmed. That means trouble for Gert because it indicates the uplift of air that creates its thunderstorms is weakening.

The Atmospheric Infrared Sounder (AIRS) instrument flies onboard NASA's Aqua satellite and takes infrared "pictures" of temperature data around the world. When Aqua flew over Tropical Storm Gert this morning, August 16, AIRS infrared data showed that cloud top temperatures had warmed in the last 24 hours. Warmer cloud tops mean that the top of the clouds are not as high as they were before (because the air gets colder the higher you go in the troposphere).

Towering thunderstorms that are not "towering" as high as they were means that the energy or convection is weakening. Convection is rapidly rising air that condenses and forms thunderstorms that make up a tropical storm.

The other thing that satellite imagery showed is that Gert has become less circular in shape which indicates that wind shear is affecting its shape. In addition, Gert's center is now exposed to influence from outer winds, which prime the system for further weakening.

Just a day before an infrared image taken on Aug. 15 at 05:41 UTC (1:41 a.m. EDT) from the AIRS instrument showed Gert had a small concentration of strong thunderstorms around the center of circulation, where cloud top temperatures were colder than -63F (-52C). Today, cloud tops are not as high, and not as cold as they were yesterday.

At 5 a.m. EDT on August 18, Gert's maximum sustained winds were near 45 mph. It was centered near latitude 36.4 north and longitude 59.6 west. Gert is speeding toward the northeast near 22 mph (35 kmh) and is expected to turn to the east-northeast and speed up.

Today, Gert is expected to keep weakening because it is battling increased wind shear and is moving into cooler waters with temperatures near 79 Fahrenheit (26 Celsius). It takes water temperatures of at least 80F (26.6C) to maintain a tropical storm's strength.

The National Hurricane Center noted that Gert is likely to lose its tropical characteristics within the next 24 hours and become post-tropical by Wednesday, August 17. At that time, Gert will move into very cool waters that are about 68F (20C).

Gert is also expected to be absorbed into a cold front by Thursday or Friday over the Northern Atlantic Ocean.

Text Credit: Rob Gutro, NASA Goddard Space Flight Center, Greenbelt, Md.



August 15, 2011

Tropical Storm Gert on Aug. 15, 2011 › Click for high resolution image
At 17:40 UTC on August 14, the MODIS instrument on NASA's Aqua satellite captured this visible image of Tropical Storm Gert (07L) in the North Atlantic Ocean, south-southeast of Bermuda. The stronger, taller thunderstorms in the center cast a shadow on the weaker ones surrounding them.
Credit: NASA Goddard MODIS Rapid Response Team

TRMM image of Tropical Storm Gert on Aug. 15, 2011 &rsaquo Click for high resolution image
Tropical Storm Gert was located southeast of Bermuda and appeared small but well organized when the TRMM satellite flew over on August 15, 2011 at 0101 UTC. A rainfall analysis from the Tropical Rainfall Measuring Mission satellite's Microwave Imager shows a comma shaped area of moderate to heavy rainfall (red) wrapping around the center of the small storm. The yellow and green areas indicate moderate rainfall between .78 to 1.57 inches (20-40 mm) per hour. Red areas indicate heavy rainfall (2 inches/50 mm per hour).
Credit: NASA/SSAI, Hal Pierce
NASA Watches Birth of Another Tropical Storm from 4 Atlantic Lows: Gert

Tropical Storm Gert was born from one of four North Atlantic Ocean low pressure areas that NASA was watching last Friday. NASA's Aqua satellite flew over Gert and noticed high, strong thunderstorms around her center of circulation. Meanwhile, two other areas of low pressure behind Gert have diminished in their chances of development.

During the early morning hours (EDT) on August 14, the low pressure area called System 94L strengthened into Tropical Depression 7 (TD7). Tropical Storm warnings were posted for Bermuda. At 10 a.m. EDT that morning, TD7 was near 28.2N 63.2W, just 300 miles (480 km) south-southeast of Bermuda. Maximum sustained winds were near 35 mph, and it was moving to the west-northwest near 7 mph. Pressure 1010 millibars.

Later in the day, at 17:40 UTC (1:40 p.m. EDT), TD7 strengthened into Tropical Storm Gert.

By Monday, August 15 at 11 a.m. EDT, Gert's maximum sustained winds had reached up to 60 mph. The National Hurricane Center (NHC) reported that tropical-storm-force winds extend outward up to 70 miles (110 km) from the center and mainly to the north and east of the center.

Gert is moving toward the north near 12 mph (19 km/h) and is expected to turn toward the north-northeast then northeast while speeding up. The NHC said that "Gert is expected to pass well to the east of Bermuda later today." At 11 a.m. EDT Gert's center was about 95 miles (155 km) east-southeast of Bermuda near 32.0 North and 63.2 West. Because tropical storm-force winds only extend out to 70 miles from the center (and away from Bermuda), the island is not expected to feel winds of that strength as Gert passes by.

At 17:40 UTC on Sunday, August 14, The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Aqua satellite captured a visible image of Tropical Storm Gert in the North Atlantic Ocean, south-southeast of Bermuda. The image revealed higher thunderstorms around the center of Gert's circulation that were casting shadows on the lower, surrounding thunderstorms. That indicates strong convection and strength within the core of the storm's heat engine. On August 15, satellite data revealed a tightening of circulation around the center, and what appeared to be "a small 6 to 8 nautical mile-wide (in diameter) eye-like feature," according to NHC. The strong convection then weakened as dry air entered.

Because Gert is smaller than the average tropical cyclone (it's less than 140 miles in diameter) it is more susceptible to being weakened by wind shear and dry air. In addition, by Wednesday morning, August 16, Gert will be moving over cooler waters which will help sap her strength.

Two other low pressure areas in the Atlantic are also being watched for possible development. One however, System 92L is too close to Tropical Storm Gert to develop on its own. The NHC gives it a "near zero percent" chance of development today.

System 93L, however, located about 325 miles east of the Lesser Antilles has a large amount of thunderstorms and clouds and has a 10 percent chance of organizing in the next two days. It continues to move westward between 15 and 20 mph and is expected to bring gusty winds and heavy rainfall over parts of the central and northern Lesser Antilles through Tuesday.

Text Credit: Rob Gutro, NASA Goddard Space Flight Center, Greenbelt, Md.



August 12, 2011

GOES image from August 12, 2011 at 1445 UTC (10:45 a.m. EDT) shows four low pressure systems: 92L, 93L, 94L and 95L › View larger image
This GOES-13 satellite image from August 12, 2011 at 1445 UTC (10:45 a.m. EDT) shows the four low pressure systems: Systems 92L, 93L, 94L and 95L that have potential to develop into a tropical depression over the weekend. System 95L is closest to the U.S. followed by System 94L, 92L and 93L.
Credit: NASA/NOAA GOES Project
TRMM saw rainfall in System 92L on August 12, 2011 at 0353 UTC. › View larger image
TRMM saw rainfall in System 92L on August 12, 2011 at 0353 UTC. System 92L was about 1000 miles east of the northern Leeward Islands. One small area of heavy rainfall (red) (2 inches/50 mm per hour) was seen on the northwestern side. Yellow and green areas indicate moderate rainfall between .78 to 1.57 inches (20 to 40 mm) per hour.
Credit: NASA/SSAI, Hal Pierce
TRMM noticed several areas of heavy rainfall (red), falling at about 2 inches (50 mm) per hour in System 93L. › View larger image
TRMM noticed several areas of heavy rainfall (red), falling at about 2 inches (50 mm) per hour in System 93L. Yellow and green areas indicate moderate rainfall between .78 to 1.57 inches (20 to 40 mm) per hour.
Credit: NASA/SSAI, Hal Pierce
System 94L, had moderate rainfall between .78 to 1.57 inches (20 to 40 mm) per hour (yellow and green areas). › View larger image
System 94L, which has a 20% chance of development on August 12, had moderate rainfall between .78 to 1.57 inches (20 to 40 mm) per hour (Yellow and green areas).
Credit: NASA/SSAI, Hal Pierce
System 95L has a high (60%) chance at developing into a tropical cyclone in the next 24 hours. › View larger image
System 95L has a high (60%) chance at developing into a tropical cyclone in the next 24 hours. System 95L was located 200 miles north of Bermuda. Yellow and green areas indicate moderate rainfall between .78 to 1.57 inches (20 to 40 mm) per hour. There were no areas of heavy rainfall (red) when TRMM captured this image very early on August, 12, 2011.
Credit: NASA/SSAI, Hal Pierce
TRMM Satellite Sees Four Possibilities for the Next Atlantic Tropical Storm

On Friday, August 12th, there were no named tropical cyclones in the North Atlantic Ocean. However, the National Hurricane Center (NHC) is now monitoring four areas in the Atlantic Ocean that have potential for developing into tropical cyclones and the TRMM satellite captured a look at their rainfall at various times in the past few days.

The Tropical Rainfall Measuring Mission or TRMM satellite is managed by NASA and the Japanese Space Agency, and can provide data on rainfall rates occurring in a tropical cyclone as well as estimate rainfall totals. On August 12, TRMM captured rainfall rates in each of the tropical candidates as the satellite flew over each one individually.

An area of disturbed weather (92L shown on the upper left) was seen by the TRMM satellite on 12 August 2011 at 0353 UTC. On August 12, System 92L was located near 17.8 North and 45.3 West, about 1000 miles east of the northern Leeward Islands. It is moving to the west-northwest at 20 mph. It has recently shown better organization, but there are no signs of a surface circulation. However, because the environmental conditions will allow for development (light wind shear and warm sea surface temperatures, System 92L has been given a 50% probability of developing into a tropical cyclone within the next 48 hours.

On August 11, 2011 at 0319 UTC, the TRMM satellite had a good view of an area of disturbed weather called System 93L. On August 12, System 93L was located 450 miles southwest of the southernmost Cape Verde Islands, near 11.3 North and 30.3 West. TRMM's Microwave Imager (TMI) and Precipitation Radar (PR) showed that this area, which has since moved to the southwest of the Verde Islands, contained lines of heavy rainfall. The NHC also gave this area a medium chance (40%) of developing into a tropical cyclone.

Another area low potential (20%) for tropical cyclone development called System 94L, was located 700 miles northeast of the northern Leeward Islands near 24.7 North and 54.7 West. System 94L was seen by the TRMM satellite on August 12, 2011 at 0350 UTC. The NHC noted that this "Slow development is possible during the next couple of days as the low moves west-southwestward or westward at about 10 mph."

The NHC also gave another area, called System 95L, has a high (60%) chance at developing into a tropical cyclone in the next 24 hours. System 95L was located 200 miles north of Bermuda near 34.8 North and 66.8 West. The TRMM satellite flew almost directly over this low pressure system early on August 12, 2011 at 0208 UTC when it was weak. By 2 p.m. EDT, the thunderstorm activity associated with it had become well-defined. The development of System 95L may be high, but it comes with a caveat. That is, it has a high chance to develop tonight (Aug. 12) or on August 13, but only before it merges with a cold front. If it does become a depression, it would be Tropical Depression 6 in the Atlantic Ocean hurricane season.

The Geostationary Operational Environmental Satellite called GOES-13 captured an image of all four low pressure systems: Systems 92L, 93L, 94L and 95L, on August 12, 2011 at 1445 UTC (10:45 a.m. EDT). Any one of these low pressure areas have the potential to develop into a tropical depression over the weekend. System 95L is closest to the U.S. followed by System 94L, 92L and 93L.

Text Credit: Hal Pierce/Rob Gutro, SSAI/NASA Goddard Space Flight Center, Greenbelt, Md.