Sudal began as a tropical depression back on the 4th of April 2004 in
the central West Pacific in the central Caroline Islands southwest of
Truk. Over the next two days Sudal slowly gathered strength becoming
a Category 1 typhoon on the 6th with maximum sustained winds estimated
at 70 knots (81 mph) by the Joint Typhoon Warning Center. The storm at
first tracked off to the northwest but then headed mainly due west
passing well south of Guam. By April 7th, Sudal had become a Category 2
storm with winds increasing to 90 knots (104 mph). The storm was then
well south of Guam and heading for the Yap Islands and Ulithi Atoll.
Sudal continued to intensify becoming a powerful Category 3 storm the
next day with winds up to 110 knots (127 mph) on the 8th as it struck the
Yap Islands. Sudal then moved northwest into the Philippine Sea and is
expected to intensify further before turning to the northeast.
The Tropical Rainfall Measuring Mission (TRMM) satellite captured these
images of Typhoon Sudal as it was strengthening into a major typhoon.
The top image was taken at 7:35 UTC on 6 April 2004. It shows the
horizontal distribution of rain rates observed by TRMM. Rain rates in
the center swath are from the TRMM Precipitation Radar (PR), the first
and only precipitation radar in space, 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).
In this first image, TRMM shows that Sudal is still rather weak and
disorganized with only a limited area of moderate rain (green area) near
the center of circulation containing an isolated stronger core (red area)
and no evidence of a closed eye. At the time, Sudal was a minimal
Category 1 typhoon. The bottom image taken 48 hours later at 7:21 UTC on
April 8 reveals a very different looking storm. Sudal now has a well-
defined, closed but still rather large eye according to the rain field.
The southwestern part of the eyewall contains an area of intense rainfall
(darker reds). This intense rain indicates that heat is being released
into the storm's center providing the fuel to drive its circulation and
possibly strengthen the storm. Rainfall rates in this image are overlaid
on visible data. The dark area seen in the visible data adjacent to the
intense rain area could be due to a subsidence hole whereby air
surrounding strong convection sinks causing clouds to evaporate. At this
time, the storm was now at Category 3 with winds at 110 knots.
TRMM is a joint mission between NASA and the Japanese space agency JAXA.