The 2004 Atlantic hurricane season continues to heat up as Tropical Storm
Bonnie, the first of two currently active storms in the Atlantic, makes
landfall along the panhandle of Florida. The Tropical Rainfall Measuring
Mission (or TRMM) satellite has followed Bonnie's progress from a weak
tropical depression east of the Lesser Antilles til landfall as a tropical
storm along the northern coast of Florida. The images and data provided
by TRMM can give valuable estimates of both storm location as well as
estimates of storm intensity to the the NOAA Tropical Prediction Center
(also known as the National Hurricane Center).
Bonnie first began as tropical depression number two (TD #2) on the 3rd of
August 2004 approximately 350 miles east of Barbados. The first image was
taken the next day at 08:14 UTC (4:14 am EDT) on 4 August 2004. 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 first and only precipitation radar in 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 reveals that TD #2 is rather
poorly organized. No banding is evident in the rain field. The system does
contain an area of heavy rain (red area) near the forward edge of the cloud
shield between Barbados and St. Lucia and St. Vincent. At the time of the
image, Bonnie was still a weak tropical depression with maximum sustained
winds estimated at just 30 knots (35 mph) by the National Hurricane Center.
The second image taken at the same time shows a vertical cross section
through the heavy rain area from the PR. The rain area is associated with
strong convection as evidenced by the deep tower (green area) above the
heavy rain (red area). The view is looking north.
TD #2 however was not able to maintain itself and degenerated back into an
open wave soon after entering the eastern Caribbean as a result of
encountering unfavorable wind shear. Over the next several days, the wave
tracked westward around the southern periphery of a subtropical ridge to
its north before emerging into the Gulf of Mexico north of the Yucatan
Peninsula. At this point the wave re-intensified into a tropical storm and
became Bonnie. The next image shows Bonnie over the north central Gulf
of Mexico as it is approaching the panhandle of Florida. The image was
taken at 22:55 UTC (6:55 pm EDT) on Wednesday August 11. TRMM shows that
Bonnie does not have an eye but that there is banding in the rain field east
of the center (green arcs). Most of the rain including some that is heavy
(red) is on the north and east side of the storm. At this time, Bonnie was
a strong tropical storm with winds of 55 knots (63 mph). Bonnie was not
able to intensify any further however as the storm was being pulled
northeastward ahead of an upper-level trough. The final image taken just a
few hours later at 03:49 UTC August 12th (11:49 pm EDT August 11) shows that
Bonnie was a small storm. An isolated area of intense rain (dark red area)
is all that remains. Winds were down to 50 knots (58 mph). Bonnie would
make landfall the next day near Apalachicola, FL as a tropical storm.
TRMM is a joint mission between NASA and the Japanese space agency JAXA.