Ketsana formed into a tropical depression several hundred miles east of
the Philippines at 18:00 UTC on 18 October 2003 and continued to organize
into a tropical storm. The Tropical Rainfall Measuring Mission (TRMM)
satellite overflew Ketsana on the 19th and captured this first image (left) at
22:23 UTC. At the time, Ketsana was a tropical storm with winds estimated
at 50 mph by the Joint Typhoon Warning Center. The TRMM image provides a
top down view of Ketsana showing rainfall rates within the storm 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). TRMM detected a large area of
intense rainfall along the southwest side of the storm’s large center
(shown by the darker reds). The heat being released near the storm center
from the area of heavy precipitation allowed Ketsana to further develop
into a typhoon.
The next image (right) was taken at 21:28 UTC on October 20th. Ketsana was now a
Category 1 storm with sustained winds estimated to be over 90 mph. The
the storm appears better organized with a closed center that is much
smaller in diameter. Moderate rain rates (green areas) surround the eye
in concentric bands. The IR data indicates that Ketsana is a fairly
symmetrical storm and does not appear to be inhibited by wind shear.
Thus, conditions remain favorable for further development. Fortunately,
Ketsana is moving away from the Philippines towards the northeast and is
not an immediate threat to any appreciable land masses.
TRMM is a joint mission between NASA and the Japanese space agency NASDA.
Images produced by Hal Pierce (SSAI/NASA GSFC) and caption by Steve Lang