Tropical Storm Polo: Discussion #7

TROPICAL STORM POLO DISCUSSION NUMBER 7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP182008
100 AM PST TUE NOV 04 2008

DEEP CONVECTION HAS INCREASED NEAR THE CENTER OF POLO DURING THE
PAST SEVERAL HOURS. HOWEVER...RECENT MICROWAVE DATA SUGGESTS THE
LOW-LEVEL CENTER IS DISPLACED TO THE WEST OF THE CONVECTION.
ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN INDICATE ABOUT
10 KT OF WESTERLY VERTICAL WIND SHEAR AFFECTING POLO...WHICH IS
PROBABLY CONTRIBUTING TO THE CURRENT STRUCTURE. QUIKSCAT DATA AT
AROUND 0200 UTC HAD TROUBLE RESOLVING THE SMALL CIRCULATION...BUT
SHOWED A COUPLE OF 35 KT VECTORS. THUS...THE INITIAL INTENSITY
REMAINS 35 KT.

THE INITIAL MOTION IS WOBBLING BETWEEN 280-285 DEGREES AT ABOUT 12
KT. THERE IS LITTLE CHANGE IN EITHER THE PREVIOUS FORECAST
REASONING OR THE FORECAST GUIDANCE. POLO IS ON THE SOUTH SIDE OF A
LOW/MID-LEVEL RIDGE...WITH A MID/UPPER-LEVEL TROUGH FORECAST TO
DEVELOP NORTHWEST OF THE CYCLONE DURING THE NEXT 72 HR. THE
GFDL...HWRF...LBAR...BAMM...AND BAMD SHOW POLO TURNING NORTHWARD IN
RESPONSE TO THIS TROUGH AS THESE MODELS KEEP A VERTICALLY COHERENT
CYCLONE. THE REMAINDER OF THE GUIDANCE CALLS FOR A WEST-
NORTHWESTWARD TO WESTWARD MOTION BASED ON THE PREMISE THAT POLO
WILL NOT MAINTAIN VERTICAL COHERENCE AS IT ENCOUNTERS THE TROUGH.
SINCE THE STORM CURRENTLY HAS A SHEARED STRUCTURE...AND THE SHEAR
IS LIKELY TO INCREASE AFTER 36-48 HR...THE FORECAST TRACK FOLLOWS
THE LATTER SET OF MODELS. THE NEW FORECAST TRACK IS SIMILAR
TO...BUT A LITTLE SOUTH OF THE PREVIOUS TRACK. IT IS IN BEST
AGREEMENT WITH THE NOGAPS...AND LIES WELL TO THE WEST OF THE
VARIOUS CONSENSUS MODELS.

SATELLITE IMAGERY SHOWS STRONG UPPER-LEVEL WESTERLY FLOW WEST OF
125W...AND THE LARGE-SCALE MODELS FORECAST POLO TO ENCOUNTER THIS
FLOW IN ABOUT 36-48 HR. THE NEW INTENSITY FORECAST CALLS FOR
SLIGHT STRENGTHENING BEFORE THE SHEAR INCREASES...FOLLOWED BY
WEAKENING AS THE CYCLONE ENCOUNTERS THE STRONGER SHEAR AND COOLER
SEA SURFACE TEMPERATURES. THE NEW INTENSITY FORECAST IS THE SAME
AS THE PREVIOUS FORECAST AND IS IN BEST AGREEMENT WITH THE LGEM
MODEL. THERE ARE TWO ALTERNATE INTENSITY SCENARIOS. FIRST...THE
GDFL CALLS FOR POLO TO BECOME A HURRICANE IN ABOUT 48 HR. THIS
APPEARS UNLIKELY AT THIS TIME. SECOND...SINCE POLO IS VERY
SMALL...IT COULD WEAKEN AND DISSIPATE FASTER THAN FORECAST WHEN IT
ENCOUNTERS THE STRONGER SHEAR.

FORECAST POSITIONS AND MAX WINDS

INITIAL 04/0900Z 9.6N 116.7W 35 KT
12HR VT 04/1800Z 10.1N 118.3W 35 KT
24HR VT 05/0600Z 10.8N 120.0W 40 KT
36HR VT 05/1800Z 11.5N 121.5W 40 KT
48HR VT 06/0600Z 11.9N 123.1W 40 KT
72HR VT 07/0600Z 12.5N 126.5W 35 KT
96HR VT 08/0600Z 13.0N 129.5W 30 KT
120HR VT 09/0600Z 13.5N 133.0W 25 KT...REMNANT LOW


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