August 2, 0823 UTC	August 2, 0823 UTC PR VERTICAL SLICE
August 3, 0412 UTC	August 3, 0412 UTC PR VERTICAL SLICE

Alex, the first named storm of the 2004 Atlantic hurricane season, has reached hurricane strength just off of the east coast of the US. The storm is expected to pass very close to the outer banks of North Carolina during the day (local time) on Tuesday the 3rd of August 2004. The Tropical Rainfall Measuring Mission or TRMM satellite was able to capture these unique images of Alex as it organized off of the southeast US coast. The images and data obtained from TRMM can provide precise estimates of the storm's location as well as estimates of the storm's intensity to the the National Hurricane Center (or NOAA Tropical Prediction Center). The first image was taken at 08:23 UTC (04:23 EDT) on 2 August 2004. It shows the horizontal distribution of rain intensity. Rain rates in the center swath are from the TRMM Precipitation Radar (PR), the first and only precipitation radar in space. The PR is able to provide fine resolution rainfall data and detailed 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). At the time of this image, Alex was still a minimal tropical storm with maximum sustained winds estimated at 35 knots (40 mph) by the National Hurricane Center. The image shows several areas of very heavy rain (dark red areas) near the center of Alex. Although the storm does not have an eye at this time, these heavy rain rates are helping to fuel the storm. As water vapor condenses into cloud droplets (which are then converted into rain), heat is released. This heat known as latent heat is what drives the storm's circulation. It is most effective when it occurs near the center of the storm. The next image was taken at the same time and shows a vertical slice through the center of the Alex by the PR looking east. It shows a deep convective tower almost 13.5 km high with very heavy rain protruding up through the freezing level (vertical dark red area). The freezing level is apparent by the horizontal bright band near the top of the moderate rain (yellow) area to the right of the tower.

The next image was taken almost a day later at 04:12 UTC (00:12 EDT) on the 3rd. A partial eyewall is now evident north of the center by the semicircle of heavy rain (dark red area). TRMM reveals that the rain field associated with Alex is very asymmetrical with the bulk of the rain appearing north of the center (blue area). Some banding is also evident in the moderate intensity rain (green arcs). The final image shows another PR cross section taken through the northern eyewall. The view is looking down towards the east. It shows a very tall convective tower nearly 16 km high (vertical blue/green area) embedded in the northern eyewall. Tall convective towers are often associated with intensifying storms. These final two images were taken just two hours before Alex became a hurricane.

Alex initially formed from a tropical depression that was spawned by an upper level low east of the Florida peninsula on the evening of 31 July 2004. The depression moved slowly northeast towards the coast of South Carolina and strengthened to become tropical storm Alex the following day, the 1st of August. Alex hovered east of Georgia the night of the 1st with very little forward speed. Alex remained a tropical storm on the 2nd but did begin to strengthen over the warm waters of the Gulf Stream and also began moving northeast parallel to the Carolina coast before intensifying into a Category 2 hurricane the next day on the 3rd.

Images produced by Hal Pierce (SSAI/NASA GSFC) and caption by Steve Lang (SSAI/NASA GSFC).