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Hurricane Season 2006: Isaac (Atlantic)
09.28.06
 
Isaac Brushes Newfoundland, Heads Toward Europe

Following the pattern established by Florence, Gordon and Helene, yet another Atlantic storm, Isaac, has formed in the Central Atlantic, intensified into a hurricane, and recurved well before approaching the East Coast. The 2006 Atlantic hurricane season has of yet continued to be a welcome relief from last year's onslaught with not a single hurricane yet to make landfall in the U.S. So far, including Isaac, there have been 9 named storms, 5 hurricanes, and 2 major hurricanes in the Atlantic--numbers very typical of an average season.

Armed with its array of passive and active sensors, the Tropical Rainfall Measuring Mission satellite (TRMM) has proven valuable for monitoring Atlantic hurricanes. This series of images was obtained by TRMM and provides a unique look at Isaac in the Atlantic.

On the afternoon of Sept. 29, conditions in the Atlantic Ocean became more favorable for storm strengthening as wind shear relaxed and the storm began to pass over warmer water. Isaac began to strengthen. By the morning of the 30th, Isaac had become a strong tropical storm.

TRMM image of Hurricane Isaac on September 30, 2006
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The first image from TRMM shows Tropical Storm Isaac at 10:24 UTC (6:24 am EDT) on the 30th. Although the storm is still quite small and is not symmetrical (note the bulk of the rain is east of the center), Isaac now has a ragged eye. The area of intense rainfall is shown as the darker red area.

3d TRMM image of Hurricane Isaac on October 1, 2006.
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The next image, taken at the same time as the previous image, provides a unique 3-D perspective of Isaac. The view is to the north. TRMM reveals that the areas of intense rain visible in the previous image are associated with deep convective (rising air) towers (towering clouds) with tops reaching up to 15 km (9.3 miles, as shown in red. Such towering clouds can indicate future strengthening especially when they are located near the core of the storm as is the case here with Isaac. This area of deep convection is responsible for releasing heat into the storm. This heating, known as latent heating, is what lowers the storm's central pressure and drives the storm's circulation. At the time of these last two images, NHC estimated Isaac's sustained winds to be 60 knots (69 mph). Isaac became a hurricane soon after.

TRMM image of Hurricane Isaac on October 1, 2006
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As Isaac moved closer to Bermuda on the night of the 30th, it began to feel the effects of a deep-layer trough and took a turn towards the north, keeping it well to the east of Bermuda. The final image shows Isaac at 12:44 UTC (8:44 am EDT) on Oct. 1 as it was passing east-northeast of Bermuda. The eye was less distinct with the southwestern portion now exposed as a result of increasing southwesterly wind shear. Isaac remained a small storm.

Isaac maintained Category 1 hurricane intensity throughout the evening of the 1st and the morning of the 2nd. By the afternoon of October 2nd, Isaac had weakened to a tropical storm. At 5:00 p.m. AST on Oct. 2, the center of Isaac was located near Latitude 47.1 north and longitude 52.2 west or about 50 miles east-northeast of Cape Race, Newfoundland, Canada. By Oct. 3, Isaac had become an extra-tropical low pressure system moving to the east-northeast in the waters of the North Atlantic Ocean. TRMM is a joint mission between NASA and the Japanese space agency JAXA. Credits: Image -- Hal Pierce, SSAI/NASA GSFC; Caption - Steve Lang, SSAI/NASA Goddard Space Flight Center



Tropical Storm Isaac's Uncertain Future Over the Weekend

TRMM captured this image of Isaac when he was Tropical Depression 9 at 6:40 am EDT on Sept. 28 in the Central Atlantic.
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The Tropical Rainfall Measuring Mission (TRMM) satellite captured this image of Isaac when he was Tropical Depression #9 at 10:40 UTC (6:40 am EDT) on Sept. 28 in the Central Atlantic. The image shows a top-down-view of the rain intensity obtained from TRMM's sensors.

Rain rates near the center are between 10 and 20 millimeters (mm) or .39 and .78 inches (as depicted in light green). Rain rates or the amount of rain falling in an hour, is obtained by two different instruments on TRMM. The Precipitation Radar which is the only radar that can measure precipitation from space, and the TRMM Microwave Imager (TMI). At the time of this image, the depression had sustained winds around 35 mph.

Isaac's Location on Sept. 29

At 11:00 a.m. EDT on Sept. 29, the center of Isaac was located about 550 miles east-southeast of Bermuda, around 29.4 north latitude and 56.2 west longitude. Isaac was packing sustained winds near 45 mph, and some strengthening is expected. Minimum central pressure has dropped to 1006 millibars from the day before, indicating a strengthening storm. Isaac is moving toward the northwest near 6 mph.

What's In Store Over the Weekend for Isaac?

As of Fri. Sept. 29, hurricane forecasters were looking at a couple of different scenarios for Isaac's future. The National Hurricane Center's Discussion noted that "By 36 to 48 hours (late Sat. or mid-day Sun. Oct. 1), the wind shear (winds that can weaken hurricanes and tropical storms) is forecast to increase," which would limit how much Isaac could strengthen. The Discussion also noted that sea surface temperatures would be cooler as Isaac moves northward. Cooler waters reduce a storm's strength. The two scenarios that forecasters are dealing with is that Isaac may or may not be absorbed into a larger low pressure (storm) system. Several computer models indicate that Isaac will be absorbed into the weather system by Mon. Oct. 2. However, the current forecast calls for Isaac to remain separate from the Low. The NHC does say that if Isaac continues to track more westward than thought, Isaac's remnants could merge with the Low. Credits: Caption- Rob Gutro, Goddard Space Flight Center and Steve Lang, SSAI/Goddard Space Flight Center Image: NASA/TRMM Hal Pierce



NASA's QuikSCAT Satellite Confirms Tropical Storm Isaac's Debut

Quikscat image of Tropical Storm Isaac taken on September 28, 2006.
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Tropical Depression #9 became Tropical Storm Isaac at 11:00 a.m. EDT on Sept. 28, 2006 according to the National Hurricane Center, and NASA's QuikSCAT satellite confirmed the transformation.

The National Hurricane Center (NHC) confirmed TD#9's transformation into a tropical storm with data from NASA's QuikSCAT satellite. The 11:00 a.m. EDT NHC report on Sept. 28 noted "A QuikSCAT pass near 0845 UTC (4:45 a.m. EDT) provides strong evidence of at least 35 knot (41 mph) winds in the system. Thus the ninth tropical storm of the year... Isaac... is born." To be classified as a tropical storm, a tropical cyclone must have sustained winds of 39 mph, and that's when it gets a name.

At 11:00 a.m. EDT on Sept. 28, the center of Isaac was located about 665 miles east-southeast of Bermuda, around 28.2 north latitude and 54.7 west longitude. Isaac was packing sustained winds near 40 mph, and some strengthening is expected. Minimum central pressure has dropped to 1008 millibars, indicating a strengthening storm. Isaac is moving toward the northwest near 8 mph.

This image from NASA's QuikSCAT satellite was captured at approximately 5 p.m. EDT (21:29 UTC) on Wed., Sept. 27. The image depicts wind speed in color and wind direction with small barbs. White barbs point to areas of heavy rain. The highest wind speeds, shown in purple, surround the center of the storm.

The QuikSCAT scatterometer sends pulses of microwave energy through the atmosphere to the ocean surface, and measures the energy that bounces back from the wind-roughened surface. The energy of the microwave pulses changes depending on wind speed and direction, giving scientists a way to monitor wind around the world. Credits: Image: NASA/JPL, Peter Falcon; Caption: Rob Gutro - Goddard Space Flight Center



Tropical Depression Nine Forms, May Become Isaac

At 5:00 p.m. EDT on Wed. Sept. 27, the ninth tropical cyclone of the Atlantic hurricane season formed about 810 miles east-southeast of Bermuda. Twelve hours later on Thurs. Sept. 28 at 5:00 a.m. EDT, the center of Tropical Depression #9 (TD #9) had moved closer, and was located 685 miles to the east-southeast of Bermuda. TD #9 is expected to stay to the east of Bermuda and curve into the North Atlantic Ocean.

On Sept. 28 at 5:00 a.m. EDT, TD#9's coordinates were 27.8 north latitude and 54.6 west longitude. It was moving to the northwest near 12 mph, but is expected to slow in forward speed. Estimated minimum central pressure was 1011 millibars. Maximum sustained winds were near 35 mph, and TD#9 is expected to strengthen. When winds reach 39 mph, TD#9 will be named Tropical Storm Isaac.

GOES spots Tropical Depression 9 in the Atlantic.
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Tropical Depression #9 (bottom right in image) can be seen in this satellite image from the National Oceanic and Atmospheric Administration's Geostationary Operational Environmental Satellite (GOES). This satellite image was captured on Thurs., Sept. 28 at 7:06 a.m. EDT. This data was processed by NASA's GOES Project at the Goddard Space Flight Center, Greenbelt, Md. Credits: Image - NASA GOES Project; Caption: Rob Gutro, Goddard Space Flight Center