Cyclone Anja hits wind shear, weakens drastically

November 17, 2009
The Tropical Rainfall Measuring Mission satellite passed over Anja on November 15 at 0904 UTC. Anja had a well defined eye and was increasing in strength from a category 2 to 3 tropical cyclone. Credit: NASA/SSAI, Hal Pierce

This morning, Cyclone Anja was a powerful Category 4 cyclone on the Saffir-Simpson scale. Wind shear has now giving Anja a strong "punch in the gut" as the storm has weakened to a Category 1 cyclone.

At 1500 UTC (10 a.m. ET) on November 17, Anja's were sustained at 75 knots (86 mph). Anja's center was located 715 miles east-northeast of La Reunion Island, near 18.3 South and 66.5 East. Anja is moving south-southwest at 12 mph. The storm seems to be spreading out as its weakening, as tropical storm force winds now extend out to 115 miles from the center (earlier today, they only extended 75 miles out from the center).

When tropical cyclone Anja formed on November 14, it was the first tropical cyclone in the southwestern . That signaled the tapering off of tropical cyclone activity and the start of tropical cyclone formation in the southern hemisphere. The Atlantic Ocean officially ends at the end of November while the southwest Indian Ocean tropical cyclone season starts on November 1 and ends on April 30.

When the Tropical Rainfall Measuring Mission (TRMM) satellite passed over Anja on November 15 at 0904 UTC it had a well-defined eye and was increasing in strength from a category 2 tropical cyclone (on the Saffir-Simpson scale) to a powerful category 3 tropical cyclone later that day. TRMM is a joint mission between NASA and the Japanese space agency JAXA.

The Tropical Rainfall Measuring Mission, or TRMM satellite passed over Anja again on November 17 at 0850 UTC showing some heavy rain around the center. TRMM data made it clear that upper level wind shear had caused Anja to weaken greatly. Credit: NASA/SSAI, Hal Pierce

The TRMM satellite passed over Anja again on November 17 at 0850 UTC. The data from TRMM made it clear that upper level wind shear (winds blowing at different directions in the atmosphere that can tear a storm apart) had caused Anja to weaken greatly from its earlier maximum category 4 intensity. Anja no longer had a well defined eye but the TRMM derived rainfall analysis showed there was still very heavy rainfall in an area near Anja's center.

Anja is predicted to continue weakening and move harmlessly toward the southeast over the open waters of the south Indian Ocean.

Source: JPL/NASA (news : web)

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