At one time Cyclone Gonu was a powerful Category 5 storm packing sustained
winds of 160 mph, according to the Joint Typhoon Warning Center, and on a
course for Oman. This made it the most powerful cyclone ever to threaten
the Arabian Peninsula since record keeping began back in 1945. Fortunately
the storm weakened significantly by the time it brushed the far eastern tip
Tropical cyclones do on occasion form in the Arabian Sea, but they rarely
exceed tropical storm intensity. Last year, Tropical Storm Mukda was the
only system to form in the region, and it remained well out to sea before
dissipating. Gonu became a tropical storm on the morning (local time) of
2 June 2007 in the east-central Arabian Sea. After some initial fluctuations
in direction, the storm settled on a northwesterly track and began to
intensify. Gonu went from tropical storm intensity on the morning of the
the 3rd to Category 2 on the night of the 3rd. By daybreak on the 4th, Gonu
was up to a Category 4 storm with winds estimated at 115 knots (132 mph).
The Tropical Rainfall Measuring Mission (TRMM) satellite was placed into
low-earth orbit in November of 1997 with the primary mission of measuring
rainfall from space; however, it has also proven to be a valuable platform
for monitoring tropical cyclones, especially over remote parts of the open
ocean. TRMM captured this image of Gonu as it was moving northwest through
the central Arabian Sea. The image was taken at 03:23 UTC on 4 June 2007.
It shows the horizontal distribution of rain intensity looking down on the
storm. Rain rates in the center of the swath are from the TRMM Precipitation
Radar (PR), while those in the outer portion are from the TRMM Microwave
Imager (TMI). The rain rates are overlaid on infrared (IR) data from the
TRMM Visible Infrared Scanner (VIRS). TRMM reveals the tell tale signs of
a potent storm. Not only does Gonu have a complete, well-formed, symmetrical
eye surrounded by an intense eyewall (innermost red ring), this inner eyewall
is surrounded by a concentric outer eyewall (outermost red and green ring).
This double eyewall structure only occurs in very intense storms. Eventually
the outer eyewall will contract and replace the inner eyewall.
The next image shows a unique 3D perspective of Gonu using data collected
from the TRMM PR from the same overpass as the previous image. Higher radar
echo tops are indicated in red. The areas of intense rain in the previous
image are associated with deep convective towers both in the innermost eyewall
and in parts of outer eyewall. The inner ring has the higher tops at this
time. Deep convective towers near the storm's center can be a precursor to
future strengthening as they indicate that large amounts of heat are being
released into the storm's core. At the time of these images Gonu was a
Category 4 cyclone. Several hours after these images were taken, Gonu reached
Category 5 intensity.
The system finally began to weaken on the morning of the 5th and was
downgraded to a Category 3 storm at 12:00 UTC on the 5th. Gonu continued to
weaken as it neared the coast of Oman. The center remained just offshore of the
northeast coast of Oman as a Category 1 storm before turning northward towards
Iran where it is expected to make landfall as a tropical storm.
Click to see a Quicktime animation (1.8MB) of Tropical Cyclone GONU FADE between visible and rainfall images.
Click to see an MPEG animation (.7MB) of Tropical Cyclone GONU FADE between visible and rainfall images.
Click to see a Quicktime 3-D FLYBY animation (37B) of Tropical Cyclone GONU from Precipitation Radar.
Click to see a MPEG 3-D FLYBY animation (1.5MB) of Tropical Cyclone GONU from Precipitation Radar.
TRMM is a joint mission between NASA and the Japanese space agency JAXA.
Images produced by Hal Pierce (SSAI/NASA GSFC) and caption by Steve Lang