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Tropical Cyclone 22S (Ilsa) Weakens Over Past 12 Hours

March 23rd, 2009 Category: Tropical Cyclones

Tropical Cyclone 22S (Ilsa) - March 23rd, 2009

Tropical Cyclone 22S (Ilsa) - March 23rd, 2009

TC 22S - enhanced image

TC 22S - enhanced image

Tropical Cyclone 22S (Ilsa), located approximately 365 nautical miles south-southwest of Cocos Island, has tracked west-southwestward at 12 knots over the past six hours. Maximum significant wave height is 20 feet.

Over the past 12 hours TC 22S has continued to weaken with significant decreases in convection. Elongation of the low level circulation center (LLCC) is apparent in animated multi-spectral imagery.

An AMSU-B pass shows mid-level dry air being entrained into the LLCC with little deep convection present. Upper level analysis indicates that Ilsa is located near an upper level subtropical ridge axis in a region of good difluent flow and low vertical wind shear.

Track of TC 22S © Univ. of Wisconsin

Track of TC 22S

Ilsa is currently tracking west-southwestward around the subtropical ridge located to the south of the system. Intensity will continue to weaken due to a combination of unfavorable surface conditions and dry air entrainment.

Ilsa Expected to Weaken Gradually While Tracking West-Southwestward

March 20th, 2009 Category: Tropical Cyclones

Tropical Cyclone 22S (Ilsa) - March 20th, 2009 © Univ. of Wisconsin

Tropical Cyclone 22S (Ilsa) - March 20th, 2009

TC 22S (Ilsa) - March 19th, 2009 © JTWC

TC 22S (Ilsa) - March 19th, 2009

Tropical Cyclone 22S (Ilsa), located approximately 530 nautical miles east-southeast of Cocos Island, has tracked westward at 10 knots over the past six hours.

The system has slightly intensified as convective bands that are wrapped around the low level circulation center have consolidated and deepened over the past 12 hours.

Enhanced poleward outflow is also evident on animated water vapor satellite imagery. Upper level analysis indicates the cyclone is tracking under an area of low vertical wind shear (VWS) along the northwestern periphery of a subtropical ridge extension.

The current position and intensity estimates are based on Dvorak satellite fixes from PGTW and APRF with T-number values at 5.5 and 5.0, respectively.

The cyclone is expected to track west-southwestward through the forecast period under the continued steering influence of the sub-tropical ridge.

TC 22S will gradually weaken as VWS will begin to increase and along-track sea surface temperatures drop to below 26 degrees Celsius. Maximum significant wave height at 200000z was 28 feet.

Tropical Cyclone 22s (Ilsa) Intensifies Rapidly

March 19th, 2009 Category: Tropical Cyclones

Tropical Cyclone 22s - March 18th, 2009

Tropical Cyclone 22s - March 18th, 2009

Track of TC 22s - March 19th, 2009 © Univ. of Wisconsin

Track of TC 22s - March 19th, 2009

Tropical Cyclone 22s (Ilsa), located approximately 720 nautical miles east-southeast of Cocos Island, has tracked southwestward at 12 knots over the past six hours. Maximum significant wave height is 18 feet.

It has passed between Jakarta, Indonesia, and Learmonth, on Australia’s North West Cape (the peninsula on the bottom right).

Animated water vapor imagery shows that the convection around the low level circulation center has further deepened and consolidated.

Upper level analysis indicates the system has tracked closer to the subtropical ridge axis and consequently, vertical wind shear (VWS) has weakened, contributing to the rapid intensification over the past 12 hours.

TC 22s - March 18th, 2009 © JTWC

TC 22s - March 18th, 2009

TC 22S will continue to track west-southwest along the northern periphery of the subtropical ridge and further intensify up to TAU 36. After that time, the system will slightly weaken with increased VWS as the ridge to the South builds.

Tropical Cyclone 19S Moves Eastward, Weakens

March 10th, 2009 Category: Tropical Cyclones

Tropical Cyclone 19S - March 10th, 2009 © CIMSS-Univ. of Wisconsin

Tropical Cyclone 19S - March 10th, 2009

TC 19S - March 9th, 2009 © JTWC

TC 19S - March 9th, 2009

Tropical Cyclone 19S, located approximately 690 nautical miles southwest of Cocos Island, has tracked eastward at 4 knots over the past 6 hours. Maximum significant wave height is 10 feet.

The cyclone has weakened considerably under the detrimental effects of increasing vertical wind shear (VWS).

The effects of the VWS are evident in a 091919z AMSRE image showing apartially exposed low level circulation center (LLCC) with the majority of the convection sheared to the Southeast.

The current intensity is based upon Dvorak estimates of 30 knots, and a 091536Z ASCAT pass showing 20 to 25 knot winds near the center.

The LLCC is forecast to become quasi-stationary under weakening steering influence as the structure of the storm degrades with increasing vertical wind shear.

This is the final warning on this system by the Joint Typhoon Warning Center, although the system will be closely monitored for signs of regeneration.

Area of Convection Flares Up

January 26th, 2009 Category: Tropical Cyclones

Area of convection in Indian Ocean - January 26th, 2009

Area of convection in Indian Ocean - January 26th, 2009

Area of convection - enhanced image

Area of convection - enhanced image

An area of convection is located approximately 335 nautical miles west-northwest of Cocos Island.

Recent animated water vapor imagery shows convection around the low level circulation center has flared up over the past six hours.

Although diffluence aloft remains good, strong vertical wind shear will hamper any significant development.

Maximum sustained surface winds are estimated at 15 to 20 knots and minimum sea level pressure at 1005mb.

The potential for the development of a significant tropical cyclone within the next 24 hours remains poor.

source JTWC

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