Compared to last year's onslaught, the 2006 Atlantic hurricane season has so far
been relatively uneventful with no storm yet having reached hurricane strength.
However, late August is generally about the time when the Atlantic hurricane season
really begins to get active. Presently Tropical Storm Debby is making its way
through the central Atlantic and poses no immediate threat to any land areas.
Known as a Cape Verde storm because of its formation in the far eastern Atlantic
near to the Cape Verde Islands, Debby began as a tropical depression on the 21st
of August 2006 from an African easterly wave that moved off of the coast of West
Africa.
|
|
The first image above shows the original easterly wave as it was exiting the African
coast. The image was taken at 0140 UTC 21 August 2006 (9:40 pm EDT 20 August 2006)
by the Tropical Rainfall Measuring Mission satellite known as TRMM. Using its
suite of active and passive sensors, TRMM is designed to measure rainfall from
space. The image shows instantaneous rain rates associated with areas of
convection within the easterly wave. Rain rates in the center swath are from the
TRMM Precipitation Radar (PR), and 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). Areas of heavy rain are shown in
darker red and are associated with the deep convection.
The disturbed area associated with the wave continued to organize over warm water
and became the 4th tropical depression of the season (TD #4) southeast of the Cape
Verde Islands. This next image on the above right from TRMM at 0125 UTC 23 August (9:25 pm 22 August)
shows TD #4 after it had passed west of the islands (note that the center of TD #4
does not fall within the PR swath in this image). Instead of scattered areas of
convection, the rain field is now organized into a coherent area with evidence of
banding (curvature) around a center, which is indicative of a closed circulation.
Soon after this image was taken, TD #4 was upgraded to a weak tropical storm and
given the name Debby.
|
|
The system then continued to track off to the northwest and out into the central
Atlantic where it has been essentially maintaining strength as a weak tropical
storm. The image on the left above was taken by TRMM at 0207 UTC 24 August (10:07 pm EDT 23 August)
as Debby was moving northwest through the central Atlantic. TRMM reveals that
Debby is a small, compact storm; however, a band of intense rain (dark red area)
is apparent north of the center and indicates an area of active convection.
The final image, obtained from TRMM PR data collected coincidentally with the
previous image, shows a complementary 3D perspective of the storm. It shows that
the intense rain visible in the previous image is associated with some relatively
deep convective towers (shown in red). This convection is what is helping to sustain
Debby's circulation. At the time of these last two images, Debby's maximum
sustained winds were estimated to be 40 knots (46 mph) by the National Hurricane
Center.
Tropical Storm Debby has been moving in a generally northwest direction around
the southern periphery of a subtropical ridge of high pressure, which is anchored
to the northeast of Debby over the Azores. Although later on Debby could possibly
become the first hurricane of the season, it is also forecast to recurve well before
it approaches the US East Coast.
