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Tropical Cyclone Felleng (13S) Now Expected to Weaken Rapidly – January 31st, 2013

13.9S 51.3E

January 31st, 2013 Category: Image of the day, Tropical Cyclones

Tropical Cyclone Felleng (13S) – January 30th, 2013

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Track of Tropical Cyclone Felleng (13S) - January 30th, 2013 © Univ. of Wisconsin

Track of TC 13S

Tropical Cyclone Felleng (13S), located approximately 310 nm northwest of La Reunion (and visible here off the coast of Madagascar), has tracked south-southwestward at 11 knots over the past six hours. Maximum significant wave height is 35 feet.

Animated infrared (IR) satellite imagery indicates that TC 13S has weakened over the past six hours due to moderate (15 to 20 knots) southwesterly vertical wind shear (VWS). IR imagery shows that deep convection is decreasing in areal extent with warming cloud top temperatures.

Despite the cloud-filled eye, a TRMM 37ghz image depicts a small microwave eye feature with the bulk of the deep convection located over the eastern semi- circle. There is high confidence in the initial position based on the TRMM image. The initial intensity is assessed at 105 knots based on Dvorak current intensity estimates ranging from 102 to 115 knots.

Felleng continues to track southward along the western periphery of a north-south oriented subtropical steering ridge (STR). The system should continue to track southward through TAU 48 then will begin to turn south-southeastward to southeastward as it rounds the southern periphery of the STR.

Dynamic model guidance is in tight agreement through TAU 72 but diverges in the extended TAUs due to minor differences in how each model depicts the orientation and strength of the STR. Additionally, GFS indicates a sharp turn south- southwestward, which is likely due to erroneous interaction with a midlatitude shortwave trough. The JTWC forecast is consistent with the previous track forecast and is positioned close to, but slightly faster than, the multi-model consensus. There is high confidence in the forecast track.

In the extended period, there are significant changes to the JTWC intensity forecast. TC 13S is now expected to weaken rapidly after TAU 48 as it encounters strong VWS associated with an approaching shortwave trough and also tracks over cool SST, which range from 25ºC to as low as 20ºC. The system is also forecast to begin extra-tropical transition (ETT) near TAU 96 and should complete ETT by TAU 120 as it becomes embedded in the midlatitude westerlies and begins to accelerate southeastward.

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