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.
TRMM is a joint mission between NASA and the Japanese space agency JAXA.
This image originally appeared on the Earth Observatory. Click here to view the full, original record.