TS CINDY

POWERFUL DENNIS STRIKES CUBA AND THREATENS THE GULF COAST

On the heels of last year's devastating hurricane season, the 2005 season is so far off to a fast and furious start especially with the emergence of of major hurricane Dennis so early in the season. Dennis is now an intense Category 4 hurricane on the Saffir-Simpson scale and is passing directly over Cuba, which was hit by Hurricane Charley in 2004. The storm is then expected to emerge into the Gulf of Mexico as a major hurricane, posing a major threat to the Gulf Coast.

Dennis began as a tropical depression (TD #4) on the night of the 4th of July 2005 in the far southeastern Caribbean just west of the windward islands. Dennis became a tropical storm the next day on the 5th as it churned its way off to the northwest through the central Caribbean. The Tropical Rainfall Measuring Mission (TRMM) satellite has been following Dennis' progress across the Caribbean. Launched back in November of 1997 to measure rainfall over the global Tropics, TRMM has proven itself to be a valuable platform for observing tropical cyclones. The first image was taken at 06:39 UTC (2:39 am EDT) on 6 July 2005. The image displays the horizontal distribution of rain intensity obtained from the TRMM satellite. Rain rates in the center part of the swath are from the TRMM Precipitation Radar (PR), the only radar that can measure precipitation from space. The PR can provide fine resolution rainfall data and details on the vertical structure. Rain rates 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). The image shows Dennis as a tropical storm with maximum sustained winds estimated at near 50 mph by the National Hurricane Center. Although it lacks an eye, the storm appears well organized at this stage with good banding evident in the rain field east of the center (green and red colored arcs) indicating the presence of a good circulation.

The next image was taken later the same day at 21:31 UTC (5:31 pm EDT) as Dennis was passing to the south of Hispanola. This image from TRMM shows that the rain field surrounding Dennis was becoming more symmetrical wrapping around the center of circulation as opposed to the previous image wherein most of the rain was distributed east of the center. Furthemore, TRMM reveals an area of intense rainfall (dark red area) very near the center of Dennis that is likely associated with a convective burst, an area of intense convection within the storm that can be a precursor to intensification. Hurricanes act as large heat engines. The fuel for these engines comes from the condensation of water vapor in the atmosphere. As water vapor condenses into the tiny cloud droplets that lead to precipitation (shown here as rainfall), heat is released. This heat, known as latent heat, is what drives the circulation of the storm. In general, the more heat that is being released, the more intense the storm will be. This heating is most effective in driving the storm if it occurs near the center of the storm as is the case shown here with Dennis. Less than an hour after this image was taken, Dennis was re-classified as a hurricane with maximum sustained winds measured at 80 mph by a hurricane hunter aircraft.

Dennis continued to steadily strengthen over the following two days becoming a powerful Category 4 hurricane with maximum sustained winds increasing to 150 mph on the 8th of July as it bore down on Cuba.