After a relatively mild start, the 2006 Atlantic hurricane season is now becoming more active with the arrival of the first major hurricane--Hurricane Gordon in the Central Atlantic. Fortunately, Gordon does not pose a risk to the US. The following series of images from the the Tropical Rainfall Measuring Mission (or TRMM) satellite chronical Gordon's development in the Atlantic.

The seventh tropical depression of the season (TD #7) formed on the evening of the 10th of September 2006 (local time) from an African easterly wave that was propagating westward across the Central Atlantic. The system further organized into a tropical storm the next day on the 11th and was given the name Gordon, the seventh named storm of the Atlantic season. This first TRMM image shows TD #7 northeast of the Leeward Islands just before it became Tropical Storm Gordon. The image was taken at 1813 UTC (2:13 pm EDT) 11 September 2006. It shows instantaneous rain rates associated with areas of convection within TD #7. Rain rates in the center swath are from the TRMM Precipitation Radar (PR), while those in the outer swath are from the TRMM Microwave Imager (TMI). The rain rates are overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS). TRMM reveals a system that is still relatively weak and immature but getting better organized. At this time TD #7 does not yet have an eyewall of any significance surrounding the center. However, there is already clear evidence of banding (curvature) in the surrounding rain field (note the arc shapes of the areas in blue and green, which denote areas of light and moderate rain, respectively). But, the banding it not very tight. This is consistent with a circulation that is closed but still not very strong.

Due to a weakness in the subtropical ridge to its north, Tropical Storm Gordon began to recurve in the Central Atlantic almost immediately and began moving in a more northerly direction. With warm waters below and improving upper-level conditions, Gordon began to intensify during the day on the 12th and reached hurricane strength that evening (local time). The next morning Gordon was still a Category 1 hurricane but poised to intensify. The next pair of images were made with TRMM data collected at 1800 UTC (2:00 pm EDT) 13 September 2006 as Hurricane Gordon was moving northward in the Central Atlantic southeast of Bermuda. Gordon is now a very different looking system compared to the previous image. Gordon now has a well-defined clear eye (dark spot in the center of the white IR cloudy region) surrounded by a complete eyewall (innermost green ring) embedded with areas of intense rain (dark red areas). The banding is now pronounced with tight curvature. These signs point to a stronger more mature circulation.

The next image, obtained from the same TRMM overpass, provides a unique 3D perspective of Gordon courtesy of the TRMM PR. The view is looking north. Surrounding the eye, TRMM reveals the presence of deep convection (shown in red) reaching to near 15 km right within the northeastern eyewall. Such towers can be an indication of future intensification especially when they are located near the core of the storm as is the case here with Gordon. This area of deep convection is responsible for releasing heat into the storm. The heating, known as latent heating, can lower the storm's central pressure, which is what drives the storm's circulation. At the time of these images Gordon's maximum sustained winds were estimated to be 80 knots (92 mph) by the National Hurricane Center (NHC), making it a strong Category 1 storm. However, just a little while after this last TRMM overpass, Gordon was upgraded to a strong Category 2 hurricane with sustained winds estimated at 95 knots (109 mph). Later that evening, Gordon would reach Category 3 intensity, making it the first major hurricane of the 2006 Atlantic season. Gordon, however, is no where near land and is expected to weaken over cooler waters as it accelerates off to the northeast in the general direction of the Azores.

LARGE [8.4mb] 3-D FLYBY QUICKTIME animation Of 15 dbz Precipitation Radar

LARGE [1.5mb] 3-D FLYBY MPEG animation Of 15 dbz Precipitation Radar

TRMM is a joint mission between NASA and the Japanese space agency JAXA. Images produced by Hal Pierce (SSAI/NASA GSFC) and caption by Steve Lang (SSAI/NASA GSFC).