Since the beginning of the satellite era in the mid-1960's, no hurricane
has ever been observed in the South Atlantic according to forecasters at
the National Hurricane Center. But on Sunday morning, March 28th, 2004,
a storm struck the Brazilian coast that may have changed all of that as
forecasters believe it to be the first hurricane ever recorded in that
region of the world. The unnamed storm made landfall near the town of
Torres just south of the resort town of Laguna in the southern Brazilian
state of Santa Catarina, about 500 miles south of Rio de Janeiro. There
were reports of winds as high as 100 kph (62 mph) in the area. So far
reports indicate that 2 persons were killed by the storm with 500 homes
destroyed and 20,000 homes damaged leaving 1500 people homeless. The
search also goes on for 11 fisherman missing at sea after their 2 boats
sank in 13-foot seas off the coast.
There is some debate, however, as to whether this storm was actually a true
hurricane. Typically, strong wind shear in this part of the South Atlantic
makes conditions unfavorable for tropical storm development. However, as
has often been seen in the North Atlantic, extratropical systems that move
over warm waters can become transformed into tropical systems and take on
tropical characteristics. This storm appears to have originated as an
extratropical low that moved off the Brazilian coast on the 20th that then
became "cutoff", meaning it became separated from the the main air flow,
on the 22nd of March. Sea surface temperatures were in the mid-70s (in
degrees Fahrenheit), about the minimum needed for tropical storm formation.
Meteorologists refer to tropical low pressure centers as warm cores because
the air in the center of the circulation is warmer then the surrounding
environmental air. Extratropical cyclones are typically cold core. The
Brazilian weather service believes that the storm was extratropical in
nature. As such a storm had thus far never been recorded in that area,
there were no aircraft available to study the storm, leaving satellites to
do the job of estimating its strength and structure.
The Tropical Rainfall Measuring Mission (TRMM) satellite is designed to
measure rainfall over the global tropics using the combination of a
microwave sensor and the first and only precipitation radar in space.
TRMM was able to capture several unique images of the storm as it made
its way through the South Atlantic. The first image (top left) was taken at 12:13
UTC on 24 March 2004. It shows the horizontal distribution of rain rates
as seen from above by the TRMM satellite. Rain rates in the center swath
are from the TRMM Precipitation Radar (PR), while rain rates in the outer
swath are from the TRMM Microwave Imager (TMI). These rain rates are
overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner
(VIRS). It shows a comma-shaped cloud pattern indicative of an area of
low pressure, but there is no indication of an eye and rain rates are
mostly weak (blue areas) with only a few, localized areas of moderate
intensity rain (green areas).
The next image (top right) taken over two days later at 12:01 UTC on the 26th shows
that the storm had become much better organized with an eye apparent in
the IR data. A long rainband continues to spiral out from the center
extending well out ahead of system as it continues to track off to the
west. The PR did not pass over the center in this image, but the TMI
indicates a broad, but weak, area of rainfall south of the center. The
third image (bottom left) was taken less than a day later at 06:11 UTC on the 27th.
The storm now has a clearly defined eye in the IR data, and this time
the PR passes directly over the center revealing a nearly complete
eyewall with mostly moderate intensity rain (green area) in the southern
portion and well-defined spiral banding in the rainfield surrounding the
eye with a couple of localized areas of heavy (red areas) rainfall. An
estimate by the AMSU (Advanced Microwave Sensor Unit) satellite put the
storm's central pressure at 979 mb, equivalent to a minimal Category 2
hurricane on the Saffir-Simpson scale. The final images (bottom right and link) were taken at
11:00 UTC on the 27th of March as the storm was nearing the coast of
southern Brazil. It now has a large, well-defined eye and a complete
eyewall though rainrates in the eyewall are not particularly intense.
The IR image also shows that the storm has a well-developed outflow
pattern as cirrus clouds extend out to the west and south of the center.
The final image shows a vertical slice through the center. It reveals
mainly moderate intensity (yellow areas) rain with an embedded area of
heavy rain (red area) in the western eyewall. A single area of intense
rain (darker red area) appears in an outer rainband east of the center.
For additional images, please visit the TRMM
TRMM is a joint mission between NASA and the Japanese space agency JAXA.