[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 071139
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 AM EST MON DEC 07 2009

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST
FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0830 UTC.

...ITCZ...
THE INTERTROPICAL CONVERGENCE ZONE AXIS IS CENTERED ALONG 7N10W
6N20W 3N35W INTO EXTREME NORTHERN BRAZIL NEAR 4N51W. SCATTERED
MODERATE CONVECTION WITHIN 240 NM N AND 120 NM S OF THE ITCZ AXIS
BETWEEN 15W AND 27W.

...DISCUSSION...

GULF OF MEXICO...
SOUTHEASTERLY WINDS CAN BE FOUND OVER THE CENTRAL AND WESTERN GULF
OF MEXICO SIPHONING BETWEEN SURFACE RIDGING OVER THE EASTERN GULF
AND TROUGHING OVER TEXAS AND NORTHERN MEXICO ASSOCIATED WITH A LOW
PRES SYSTEM PASSING THROUGH THE MID MISSISSIPPI VALLEY. THE 0306 UTC
ASCAT PASS SHOWED THE STRONGEST WINDS WERE OVER THE NW GULF AT 20 TO
25 KT. A PRE-FRONTAL TROUGH LIES ONSHORE FROM LITTLE ROCK...ARKANSAS
SW TO THE COAST NEAR PALACIOS...TEXAS. COASTAL U.S. RADARS SHOW THE
BULK OF THE SHOWER AND THUNDERSTORM ACTIVITY LIES JUST E OF THIS
TROUGH ALONG THE SE TEXAS AND SW LOUISIANA COASTS. THE LOW PRES
SYSTEM N OF THE AREA IS EXPECT TO RACE NORTHEASTWARD
TODAY...ALLOWING WINDS TO DIMINISH A NOTCH IN THE NW GULF...BUT THE
GENERAL PATTERN WILL REMAIN THE SAME WITH RIDGING OVER THE EASTERN
GULF AND LINGERING TROUGHING ALONG THE NW GULF COAST. BY TUE...THE
UPPER PATTERN IN THE NORTHERN STREAM WILL BECOME MORE AMPLIFIED AS A
STRONG NEW SURFACE SYSTEM MAKES ITS WAY THROUGH THE GREAT BASIN AND
ROCKIES. SOUTHERLY WINDS IN ADVANCE OF THIS SYSTEM WILL AGAIN EXCEED
20 KT OVER THE WESTERN GULF AND NORTHERLY MOISTURE TRANSPORT WILL
INCREASE...WITH SHOWERS AND THUNDERSTORMS INCREASING OVER THE LOWER
MISSISSIPPI VALLEY THROUGH THE DAY.

CARIBBEAN SEA...
THE CARIBBEAN CONTINUES TO BE MARKED BY STRONG SUBSIDENCE AND
LIMITED MOISTURE...BRINGING TRANQUIL WEATHER TO MUCH OF THE AREA.
NUMEROUS SHOWERS CAN BE FOUND ON THE ROUTE BETWEEN THE
NICARAGUA/HONDURAS BORDER TO THE WINDWARD PASSAGE INCLUDING JAMAICA
AS WELL AS NEAR THE VENEZUELAN COAST E OF 70W WHILE MORE SCATTERED
TRADE WIND SHOWERS CAN BE FOUND THROUGH THE REMAINDER OF THE EASTERN
CARIBBEAN. THE 0122 AND 0302 UTC ASCAT PASSES SHOWED THE WIND FIELD
IN THE CARIBBEAN WERE STRONGEST N AND NW OF THE COAST OF
COLOMBIA...WITH 20 TO 25 KT WINDS GENERATED BY THE PRES GRADIENT
BETWEEN LOW PRES OVER COLOMBIA AND THE SURFACE RIDGE STEMMING FROM A
1029 MB HIGH PRES CENTER NEAR OCEAN CITY...MD AND EXTENDING SOUTH
THROUGH THE EASTERN GULF OF MEXICO TO THE YUCATAN CHANNEL. EXPECT
THIS PATTERN TO REMAIN IN PLACE UNTIL TUE WHEN THE RIDGING IN THE
EASTERN GULF OF MEXICO IS ERODED BY THE NEXT SYSTEM PULLING E ACROSS
THE ROCKIES...MAKING THE RIDGING STEMMING FROM WEAKER HIGH PRES OVER
THE CENTRAL ATLANTIC AND EXTENDING ZONALLY ALONG 24N E OF THE
BAHAMAS THE PRIMARY CONSIDERATION FOR THE PRES GRADIENT OVER THE
CARIBBEAN. LOOK FOR WINDS TO WEAKEN A NOTCH OVER THE CENTRAL
CARIBBEAN TUE AS A RESULT.

ATLANTIC OCEAN...
A COLD FRONT LIES OVER THE SW N ATLANTIC FROM 31N59W TO 28N68W AND
THEN BECOMES A WARM FROM TO 28N73W TO 26N78W. THE ASCAT PASS FROM
0126 UTC SHOWED THE NE TO E WINDS HAVE GENERALLY DROPPED BELOW 20 KT
N OF THE FRONT. THE GOES TOTAL PRECIPITABLE WATER IMAGERY SHOWS
MOISTURE OVERRUNNING THIS SURFACE BOUNDARY. NIGHT CHANNEL AND
CONVENTIONAL INFRARED SATELLITE IMAGERY CONFIRM THIS BY SHOWING
MULTI-LAYERED CLOUDINESS AND SHOWER ACTIVITY MAINLY N OF THE FRONT.
IN ADDITION...RADAR OVER FLORIDA SHOWS A BAND OF SHOWERS IN THE
OVERRUNNING REGION OF THE WARM FRONT FROM NORTH OF TAMPA BAY TO
NORTH OF CAPE CANAVERAL WITH SHOWERS PASSING EASTWARD OFFSHORE UNDER
MID TO UPPER LEVEL WESTERLY STEERING FLOW. THE PORTION OF THIS FRONT
S OF 28N IS EXPECTED TO STALL AND WEAKEN TODAY WHILE THE REMAINDER
OF THE FRONT CONTINUES TO CHARGE EASTWARD INTO THE CENTRAL ATLANTIC.
FARTHER E...A DISSIPATING COLD FRONT LIES FROM 31N22W TO 25N35W. THE
TROUGHING DUE TO THIS BOUNDARY HAD WEAKENED THE EASTERN EDGE OF THE
SURFACE RIDGE CENTERED BETWEEN THE 1022 MB HIGH PRES NEAR 33N29W AND
THE 1024 MB HIGH PRES NEAR 28N44. IN ADDITION...THE ADVANCING COLD
FRONT OVER W WATERS IS ERODING THE RIDGE FROM THE WEST. THIS RIDGING
IS EXPECTED TO WEAKEN FURTHER AND SHIFT SOUTHWARD AS THE ADVANCING
PORTION OF THE COLD FRONT ENCROACHES UPON IT. TO THE WEST OF THIS
RIDGE LIES A POSITIVELY TILTED UPPER TROUGH THAT WILL PINCH OFF AN
UPPER LOW SOUTH OF THE CANARY ISLANDS BY TUE. A 100 KT WESTERLY
UPPER JET LIES ON THE SE EDGE OF THIS TROUGH AND IS TRANSPORTING
TROPICAL MOISTURE ALOFT NORTHEASTWARD TOWARD WEST AFRICA...WITH A
WIDE BAND OF CIRRUS FOUND ALONG AND S OF THE ROUTE FROM THE FRENCH
GUIANA TO THE CAPE VERDE ISLANDS N OF THE ITCZ AS A RESULT.
DIFFLUENCE IN THE REAR RIGHT QUADRANT OF THIS UPPER JET IS CURRENTLY
SUPPORTING SCATTERED MODERATE SHOWERS AND THUNDERSTORMS ALONG THE
ITCZ AXIS BETWEEN 15W AND 27W.

$$
SCHAUER




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