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 of Oman.

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 (SSAI/NASA GSFC).