animation (1.6 MB MPEG)
After originating in the eastern Atlantic west of the Cape Verde Islands,
Isabel became the second major hurricane of the 2003 Atlantic season when
it was declared a Category 3 storm by the National Hurricane Center on
September 8. Since that time, Isabel has strengthened tremendously into
an extremely powerful Catergory 5 hurricane with winds estimated at 160 mph.
During its journey across the central Atlantic, the Tropical Rainfall
Measuring Mission (TRMM) satellite has been able to capture some astounding
images of Isabel.
The first image (top left) was taken on 10 September at 21:41 UTC (5:41 pm AST) when
Isabel was still a Category 4 storm with winds estimated at 140 mph. The
image provides a top down view of Isabel with rainfall rates from the TRMM
Precipitation Radar (PR) in the inner swath and the TRMM Microwave Imager
(TMI) in the outer swath overlaid on Infrared (IR) data from the TRMM
Visible Infrared Scanner (VIRS). It shows that Isabel has a very well-
defined eye with an nearly concentric ring of intense rainfall rates (seen
by the darker reds) that are providing heat energy to fuel the storm
directly into the core. There is also excellent cirrus outflow in all
quadrants especially to the south and west indicating that environmental
conditions continue to be favorable for further strengthening.
The next image (top right) was taken at 4:56 UTC (12:56 am AST) on September 12th.
Isabel was now a powerful Catergory 5 storm with sustained winds estimated
to be 160 mph with gusts up to 195 mph by the National Hurricane Center.
Isabel continues to be a very symmetrical storm with good cirrus outflow.
The eye is now slightly larger and is again surrounded by a nearly
concentric ring of intense rainfall. This TRMM image also shows an
amazing view of Isabel's inner eyewall structure. The inside edge of
the eyewall contains several waves. These waves are actual mesovortices
being shed from the eyewall. The next image (bottom left) provides a close-up view
of the mesovortices as seen by TRMM.
The last image (bottom right) is a visible image of Isabel taken by GOES at 12:44 UTC
(8:44 am AST) again on September 12th. It also shows the mesovortices
as rings of cloud in the eye. Where the rings border each other can be
seen as what appear to be cloud "spokes". The five spokes indicate that
there are 5 mesovortices inside the eye of this very powerful hurricane.
TRMM is a joint mission between NASA and the Japanese space agency NASDA.