[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 291745
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST THU NOV 29 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 6N9W 5N21W 5N35W 4N45W 1N51W.
THE AXIS IS FAIRLY ACTIVE TODAY WITH SCATTERED MODERATE
CONVECTION WITHIN 180 NM N AND 120 NM S OF THE AXIS BETWEEN
14W-43W.

DISCUSSION...

GULF OF MEXICO...
A FEW WEAK SFC FEATURES ARE LOCATED IN THE GULF BUT NONE OF
THESE AMOUNT TO MUCH SENSIBLE WEATHER. ONE OF THESE IS A
COLD FRONT IN THE FAR NW CORNER ANALYZED FROM SRN LOUISIANA TO
EXTREME S TEXAS. THE FRONT IS VERY DRY AND WEAK IN NATURE WITH
ONLY THIN BROKEN CLOUDINESS ALONG IT. SLIGHTLY DENSER CLOUDINESS
...WHICH LIKELY CONTAIN ISOLATED SHOWERS...LIES TO THE S OF THE
FRONT IN THE NW GULF FROM 25N-29N W OF 91W. SIMILAR CLOUDS ARE
WITHIN 60 NM OF THE MEXICAN COAST S OF 25N ASSOCIATED WITH A
WEAK COASTAL LOW-LEVEL TROUGH. ANOTHER WEAK LOW-LEVEL TROUGH IS
ANALYZED ALONG 84W/85W FROM 25N-29N. VISIBLE IMAGERY SHOWS A
SLIGHT TWIST TO THE FAINT CLOUDINESS IN THE AREA WHICH IS
CONFIRMED BY THE WEAK CYCLONIC TURNING EVIDENT IN THE SFC OBS.
IN THE MID AND UPPER LEVELS...RIDGING DOMINATES THE PATTERN
EXTENDING NW FROM THE CARIBBEAN REACHING A CREST NEAR 29N89W. A
RETREATING WEDGE OF VERY DRY AIR IS OVER THE FL PENINSULA SOON
TO BE REPLACED BY PATCHY HIGH LEVEL CLOUDINESS.

CARIBBEAN SEA...
MAINLY QUIET CONDITIONS PREVAIL ACROSS THE CARIBBEAN SUPPORTED
BY WIDESPREAD DRY STABLE AIR. THE DRIEST AIR IS E OF 80W WHERE
THE UPPER FLOW BECOMES INCREASINGLY CONFLUENT TO THE SW OF A
BROAD CENTRAL ATLC TROUGH. THERE IS SOME PATCHY CLOUDINESS AND
POSSIBLE SCATTERED SHOWERS ACROSS THE FAR SW CARIB S OF 12N W OF
76W...AIDED BY SLY UPPER FLOW ON THE RETURN SIDE OF AN ELONGATED
RIDGE WHICH RUNS FROM COLOMBIA THRU THE YUCATAN CHANNEL. TRADE
WINDS REMAIN ON THE STRONG SIDE ACROSS THE S PORTION. THE
STRONGEST WINDS ARE AROUND 25 KT NEAR THE COLOMBIAN COAST AS
NOTED IN A RECENT QSCAT PASS. TYPICAL STREAMS OF QUICK MOVING
SHALLOW SCATTERED SHOWERS ARE BEING STEERED BY THE NE TO E
LOW-LEVEL FLOW...ESPECIALLY E OF 75W.

ATLANTIC OCEAN...
A HIGHLY ELONGATED MID TO UPPER RIDGE EXTENDS NE FROM THE
CARIBBEAN COVERING MUCH OF THE AREA W OF 70W. ABUNDANT
SUBSIDENCE IS EMBEDDED IN THE RIDGE PROVIDING FAIR WEATHER
ACROSS THE WRN ATLC. IN THE LOWER LEVELS...SFC HIGH PRES
EXTENDING SSW FROM THE MID-LATITUDES DOMINATES THE PATTERN. THE
TAIL END OF A WEAK COLD FRONT BARELY CLIPS THE AREA ENDING NEAR
31N63W ONLY PRODUCING BROKEN CLOUDINESS IN ITS VICINITY. A WEAK
SFC TROUGH IS OFF THE E COAST OF FLORIDA ALONG 79W/80W FROM
28N-31N. WEAK CONVERGENCE NEAR THE BOUNDARY IS GENERATING NARROW
N-S LINES OF SCATTERED SHOWERS WITHIN 60 NM OF THE AXIS AS NOTED
IN DOPPLER RADAR.

THE MAIN FEATURE IN THE CENTRAL ATLC IS A VERY BROAD MID TO
UPPER TROUGH WHICH HAS BEEN NEARLY STATIONARY OVER THE PAST
COUPLE OF DAYS. THE ONCE WELL DEFINED CUT OFF EMBEDDED IN THE
TROUGH HAS BEGUN TO OPEN UP BUT A SERIES OF SHORTWAVES UPSTREAM
WILL LIKELY HELP TO MAINTAIN THE DEPTH OF THE TROUGH OVER THE
NEXT DAY OR SO. AN ASSOCIATED WWD MOVING LOW-LEVEL TROUGH IS
ANALYZED ALONG 29N48W 21N54W 12N55W. THIS BOUNDARY IS A LITTLE
BETTER DEFINED TODAY IN THE SURROUNDING SHIP/BUOY DATA WHICH
REVEALS SOME CYCLONIC TURNING IN THE WINDS AND LOWER PRES NEAR
THE AXIS. THE COMBINATION OF INSTABILITY ALOFT AND LOW-LEVEL
CONVERGENCE IS PRODUCING SCATTERED SHOWERS AND ISOLATED TSTMS
MAINLY E OF THE SFC TROUGH FROM 20N-26N BETWEEN 40W-51W.

SFC RIDGING EXTENDING SWD FROM A 1030 MB HIGH IN THE AZORES
REMAINS WELL IN CONTROL ACROSS THE E ATLC ALLOWING MODERATE TO
FRESH TRADES TO BE UNINTERRUPTED. THE MID-UPPER PATTERN HAS
BECOME A LITTLE MORE AMPLIFIED THAN THE ZONAL FLOW OVER THE PAST
COUPLE OF DAYS DUE TO A RIDGE STRETCHING NWD FROM THE EQUATOR
ALONG EQ23W 19N29W 31N34W AND AN ELONGATED TROUGH EXTENDING SW
FROM A DEEP LAYERED LOW IN THE SRN MEDITERRANEAN TO ABOUT
29N28W. A SWIFT SW TO W JET BRANCH BETWEEN THESE FEATURES IS
ADVECTING PATCHY HIGH LEVEL CLOUDINESS S OF 22N AND AIDING IN
THE DEVELOPMENT OF CONVECTION IN THE ITCZ BETWEEN 18W-42W.

$$
CANGIALOSI




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