[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 121144
TWDAT

TROPICAL WEATHER DISCUSSION...
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 AM EST THU DEC 12 2007

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN
SECTIONS OF SOUTH AMERICA...AND THE 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
1115 UTC

...SPECIAL FEATURE...
TROPICAL STORM OLGA HAS EMERGED INTO THE WINDWARD PASSAGE NEAR
19.3N 73.8W AT 12/1200 UTC ABOUT 55 NM SOUTH-SOUTHEAST OF THE
EASTERN TIP OF CUBA AND ABOUT 95 NM WEST-NORTHWEST OF
PORT-AU-PRINCE HAITI MOVING W AT 17 KT. ESTIMATED MINIMUM
CENTRAL PRESSURE IS 1007 MB. MAXIMUM SUSTAINED WIND SPEED HAS
DECREASED TO 40 KT WITH GUSTS TO 50 KT. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
AND THE NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS
MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS. THE HIGH TERRAIN OF
HISPANIOLA APPEARS TO HAVE TAKEN A TOLL ON OLGA WITH SATELLITE
IMAGERY SHOWING LITTLE CONVECTION NEAR THE CENTER AND SOME
DECREASE IN ORGANIZATION OF THE WEAK TO MODERATE CONVECTION N OF
THE CENTER FROM 20N-23N BETWEEN 67W-72W. IN ADDITION...THE
LOW-LEVEL CIRCULATION HAS BECOME DISRUPTED FROM THE TOPOGRAPHY
AND THERE APPEARS TO BE ANOTHER VORTICITY MAXIMUM TO THE S OF
HAITI. WEAKENING TO A REMNANT LOW IS EXPECTED IN THE NEXT DAY OR
TWO AS NORTHWESTERLY SHEAR DEVELOPS OVER THE SYSTEM. HEAVY
RAINFALL IS A HIGH CONCERN WITH LIFE-THREATENING FLASH FLOODS
AND MUDSLIDES POSSIBLE IN PUERTO RICO AND HISPANIOLA. SEE THE
CARIBBEAN DISCUSSION BELOW FOR MORE DETAILS.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 6N10W 4N30W 5N45W 4N52W. SCATTERED
MODERATE CONVECTION IS WITHIN 180 NM S OF THE AXIS E OF 13W AND
WITHIN 120 NM N OF THE AXIS BETWEEN 26W-31W. SCATTERED SHOWERS
AND TSTMS ARE ELSEWHERE WITHIN 240 NM N AND 90 NM S OF THE AXIS
BETWEEN 20W-50W.

DISCUSSION...
GULF OF MEXICO...
A MID TO UPPER LEVEL RIDGE REMAINS PARKED OVERHEAD WHILE A
WEAKENING UPPER LOW CONTINUES ITS SLOW W MOVEMENT OVER THE
BAHAMAS. THIS PATTERN IS ENHANCING DRY STABLE AIR ALOFT
...ESPECIALLY S OF 28N E OF 90W...SUPPRESSING THE FORMATION OF
ANY DEEP CLOUDINESS. IN THE LOWER LEVELS...SIMILAR SETUP AS THE
PAST COUPLE OF DAYS WITH RIDGING EXTENDING SW INTO THE AREA FROM
A W ATLC SFC RIDGE. WINDS ARE MAINLY MODERATE OUT OF THE E TO
SE...EXCEPT SLY IN THE NW CORNER AHEAD OF A SLOW MOVING COLD
FRONT OVER TEXAS. MILD AND RATHER HUMID WEATHER WITH THE CHANCE
OF LIGHT ISOLATED SHOWERS IS THE RESULT OF THIS FLOW PATTERN.
HOWEVER...THIS WILL BEGIN TO CHANGE AS A COUPLE OF FRONTS
PROPAGATE ACROSS THE AREA LATER THIS WEEK AND OVER THE WEEKEND.

CARIBBEAN SEA...
BANDS OF HEAVY RAIN...ASSOCIATED WITH TROPICAL STORM OLGA...IS
AFFECTING THE ISLAND OF HISPANIOLA...ESPECIALLY IN THE HIGH
TERRAIN AND ONSHORE AND UPSLOPE REGIONS. RAINFALL AMOUNTS OF 4
TO 6 INCHES ARE POSSIBLE OVER THIS ISLAND WITH ISOLATED MAXIMUM
TOTALS OF 10 INCHES. SHOWER AND TSTM ACTIVITY IS DIMINISHING
OVER PUERTO RICO WITH DOPPLER RADAR DETECTING ONLY SCATTERED
PATCHES OF ACTIVITY IN THE VICINITY. DOPPLER DERIVED RAINFALL
TOTALS REVEAL 8+ INCHES OVER THE CORDILLERA CENTRAL AND AREAS OF
THE N COAST. SEE SPECIAL FEATURE SECTION FOR MORE DETAILS ON
OLGA. ELSEWHERE...SCATTERED MODERATE CONVECTION HAS BLOSSOMED
OVER AND JUST E OF THE WINDWARD ISLANDS S OF 13N. LIGHTER
ISOLATED SHOWERS HAVE SPREAD W TO ABOUT 66W S OF 14N. THIS
ACTIVITY IS ASSOCIATED WITH SLIGHT DIFFLUENCE ALOFT AND A
LOW-LEVEL ELY SURGE. THE REMAINDER OF THE REGION IS EXPERIENCING
MOSTLY FAIR WEATHER BENEATH MODERATE TO STRONG SUBSIDENCE...
ESPECIALLY N OF 17N W OF 78W WHERE THE ENVIRONMENT APPEARS
DRIEST. TRADE WIND FLOW IS LIGHTER TODAY ACROSS MUCH OF THE S
CENTRAL AND SE CARIB DUE TO THE WEAKNESS BROUGHT ABOUT BY OLGA.
STRONG NELY WINDS PERSIST N OF 16N W OF 73W.

ATLANTIC OCEAN...
TROPICAL STORM OLGA IS THE WEATHER HIGHLIGHT ACROSS THE ATLC
DISCUSSION AREA. SEE SPECIAL FEATURE SECTION FOR DETAILS.
OTHERWISE...THE BASIN IS FAIRLY QUIET THIS MORNING WITH MODERATE
TO STRONG RIDGING DOMINATING THE SFC PATTERN SUPPORTED BY A PAIR
OF 1026 MB HIGHS NEAR BERMUDA AND ANOTHER 1026 MB ABOUT 250 NM W
OF THE IBERIAN PENINSULA NEAR 39N15W. THERE IS A SLIGHT WEAKNESS
IN THE RIDGE BETWEEN 30W-45W DUE TO A COLD FRONT N OF THE AREA
AND NEAR THE AFRICAN COAST N OF 20N DUE TO INVERTED TROUGHING
ASSOCIATED WITH AN UPPER LOW. WINDS ARE STRONGEST NEAR OLGA AS
TROPICAL STORM FORCE WINDS EXTEND WITHIN 225 NM IN THE N
SEMICIRCLE. A LARGE AREA OF 20-30 KT NE TO E WINDS EXTEND NWD TO
27N BETWEEN 60W-78W DUE TO THE TIGHT PRES PATTERN BETWEEN THE
BERMUDA HIGH AND OLGA.

THE MID AND UPPER PATTERN CONSISTS OF A LONGWAVE RIDGE/TROUGH
IN THE SUBTROPICS AND FAIRLY ZONAL FLOW ACROSS THE TROPICAL
BELT. CONVECTION HAS BLOSSOMED THROUGHOUT THE OVERNIGHT HOURS S
OF 13N BETWEEN 54W-62W AIDED BY THE STRONG ZONAL FLOW ALOFT AND
A LOW-LEVEL ELY WIND SURGE. DEBRIS HIGH LEVEL MOISTURE HAS
SPREAD WELL E TO ABOUT 28W MOSTLY S OF 12N. THE ONLY OTHER AREA
OF ORGANIZED CLOUDINESS IS NEAR OUR N BORDER N OF 30N BETWEEN
31W-41W ASSOCIATED WITH A FAIRLY VIGOROUS SHORTWAVE AND COLD
FRONT.

$$
CANGIALOSI


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