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Typhoon Vamco (11W)

18.7N 157.1E

August 20th, 2009 Category: Tropical Cyclones

Typhoon Vamco - August 20th, 2009

Typhoon Vamco - August 20th, 2009

Enhanced image of Vamco

Enhanced image of Vamco

Track of Typhoon Vamco - August 20th, 2009 © Univ. of Wisconsin

Track of Typhoon Vamco

Typhoon 11W (Vamco), located approximately 970 nm east-southeast of iwo to, has tracked north-northwestward at 02 knots over the past six hours.

The steering environment remains weak as the mid-level subtropical ridge (str) located to the east-northeast of Vamco has been interrupted by an upper level tropical tropospheric trough (TUTT) cell that has developed from the upper level into the mid-level. Upper level analysis indicates the poleward outflow from Vamco into another TUTT cell located to the north remains well defined and in association with the equatorward outflow channel has helped to increase the maximum intensity over the past 06 hours.

The vertical wind shear (VWS) has remained low over the past 12 hours and the sea surface temperatures (SST) have helped to fuel the recent increase in intensity. The current position and intensity are based on animated multispectral satellite imagery, and on dvorak estimates from PGTW, KNES, and RJTD.

Vamco is expected to remain in a weak steering environment through the next 48 hours as the tutt cell to the east-northeast begins to move northward towards the mid-latitude flow and get absorbed. This will allow the mid-level str to build westward increasing track speed for Vamco beyond tau 48.

An approaching mid-latitude trough will track north of the STR axis, creating a weakness around tau 72 allowing a turn northward. The VWS and SST will remain favorable for continued development through tau 72. The upper level environment will maintain in a dual outflow pattern through the early portion of the forecast helping to enhance and sustain the intensity of Vamco through tau 72.

An approaching mid-latitude trough is forecast to track along the northern axis of the STR, creating a weakness in the STR around tau 72 allowing for a more northward track. As the trough digs southward increased upper level outflow will be captured in the mid-latitude flow, helping to slow the weakening of Vamco through tau 120. Additionally, the digging trough will enhance to break in the str allowing Vamco to recurve along the orthwestern periphery of the str. Increased VWS, decreased SST values, and less favorable ocean heat content will be the primary factors causing the system to begin weakening beyond tau 96.

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