June 14, 2007 At one time Cyclone Gonu was a powerful Category 5 storm packing sustained winds of 160 mph (139 knots), according to the Joint Typhoon Warning Center, making 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, but it still threatened petroleum shipping lanes in the northern part of the Arabian Sea that are unprepared for such an intense cyclone.
While tropical cyclones occasionally form in the Arabian Sea, they rarely exceed tropical storm intensity. In 2006, Tropical Storm Mukda was the only tropical 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 Sat., Jun. 2, in the east-central Arabian Sea. After some initial fluctuations in direction, it settled on a northwesterly track and began to intensify. Gonu strengthened from tropical storm intensity on the morning of June 3 to Category 2 that night. By daybreak on June 4, Gonu had intensified to Category 4 with winds estimated at 132 mph (115 knots).
NASA's Tropical Rainfall Measuring Mission (TRMM) satellite captured an image of Gonu as it was moving northwest through the central Arabian Sea. Taken on Mon., Jun. 4 at 0323 UTC (11:23 p.m. EDT on Sun., Jun. 3), it shows the horizontal distribution of rain intensity looking down on the storm. 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.
Another image provides a unique 3-D perspective of Gonu using data collected from the TRMM Precipitation Radar 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 later, Gonu reached Category 5 intensity.
The system finally began to weaken during the night of June 4 and was downgraded to a Category 3 storm at 1200 UTC (8:00 a.m. EDT) on June 5.
NASA's Quikscat spacecraft also observed Gonu. Its SeaWinds scatterometer, a specialized microwave radar, measured near-surface wind speed and direction within the storm.
Gonu continued to weaken as it neared the coast of Oman. The center remained just offshore Oman's northeast coast as a Category 1 storm before turning northward towards Iran, where it is expected to make landfall as a tropical storm.
TRMM is a joint mission between NASA and the Japanese space agency JAXA. QuikScat is managed by NASA's Jet Propulsion Laboratory. Images produced by Hal Pierce (SSAI / NASA GSFC). Caption by Steve Lang (SSAI / NASA GSFC), Mike Bettwy (RSIS / NASA GSFC), and NASA/JPL/QuikScat Science Team.
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