[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 310004
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST FRI DEC 30 2011

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...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL
ANALYSIS.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 05N10W TO
05N14W....WHERE IT TRANSITIONS TO THE INTERTROPICAL CONVERGENCE
ZONE...CONTINUING ON TO 05N20W TO 03N26W TO 03N39W TO THE
BRAZILIAN COAST ALONG THE EQUATOR NEAR 50W. SCATTERED MODERATE
ISOLATED STRONG CONVECTION WAS OCCURRING WITHIN 180 NM N AND 90
NM S OF AXIS E OF 22W AND BETWEEN 27W AND 44W.

...DISCUSSION...

GULF OF MEXICO...
WATER VAPOR IMAGERY INDICATES WEST-SOUTHWESTERLY UPPER LEVEL
FLOW OVER MOST OF THE GULF THIS EVENING AS DOWNSTREAM RIDGING
PREVAILS ACROSS NORTHERN S AMERICA AND THE EASTERN TWO-THIRDS OF
THE CARIBBEAN. AN UPPER LEVEL SHORTWAVE TROUGH HAS BEGUN TO
SWEEP SEWD OFF THE UPPER TEXAS COAST...EXTENDING FROM AN UPPER
CYCLONE APPROACHING SRN LAKE MICHIGAN...SSW ALONG THE
MISSISSIPPI RIVER BASIN TO SE TEXAS NEAR 28N97W AND CONTINUING
WSW ACROSS NRN MEXICO TO NEAR 26N107W. THE PARENT TROUGH AND
CYCLONE WILL CONTINUE E AND SHARPEN DURING THE NEXT 24-36
HOURS...DRAGGING A WEAK MID TO UPPER LEVEL TROUGH EWD ACROSS N
PORTIONS OF THE GULF ALONG ABOUT 28N. A WEAK CONVERGENCE ZONE
AHEAD OF THE TROUGH WAS MOVING E-NE ACROSS PORTIONS OF THE SE
U.S. AND NRN FLORIDA AND WILL YIELD WEAK AND SHALLOW CONVECTION
ACROSS THE FAR NE GULF AND NRN FLORIDA OVERNIGHT. A WRN
EXTENSION OF THE ATLC SURFACE RIDGE EXTENDED WWD ACROSS THE
GULF...ANCHORED ON A 1020 MB HIGH CENTERED NEAR THE SW FLORIDA
COAST NEAR 27N82W...EXTENDING W TO THE SE TEXAS COAST. THIS WEAK
RIDGE WILL REMAIN IN PLACE THROUGH LATE SATURDAY. THE NEXT COLD
FRONT IS EXPECTED TO ENTER THE NW GULF WATERS SUNDAY MORNING AND
SINK S-SE ACROSS THE BASIN...AND INTRODUCE FRESH TO STRONG NORTH
TO NORTHEAST WINDS BASIN-WIDE THROUGH TUESDAY. BRIEF AND MINIMAL
GALES ARE SUGGESTED BY GLOBAL MODELS ALONG THE LOWER MEXICAN
COAST OF THE WRN BAY OF CAMPECHE MONDAY AFTERNOON-EVENING.

CARIBBEAN SEA...
A BROAD TROUGH-RIDGE-TROUGH UPPER PATTERN SPANS FROM THE
TROPICAL EPAC ACROSS THE CARIBBEAN TO THE TROPICAL E ATLC. A
BROAD UPPER LEVEL RIDGE IS ACROSS THE CARIBBEAN...WITH MEAN AXIS
ALONG 62W-63W...WITH WATER VAPOR IMAGERY SUGGESTING UPPER
CONVERGENCE AND SUBSIDENCE EXTENDING BETWEEN THE TROPICAL NORTH
ATLC FROM BEYOND 50W TO CENTRAL AMERICA AND SOUTHERN MEXICO
ALONG 96W. WITH A STABLE ATMOSPHERE ALOFT...THE BASIN REMAINS
TRANQUIL CONVECTIVELY. HOWEVER...AT THE SURFACE...A MODEST
PRESSURE GRADIENT BETWEEN THE ATLC AND GULF OF MEXICO RIDGE AND
LOWER PRESSURE OVER NORTHERN SOUTH AMERICA IS PRODUCING STRONG
E-NE TRADES IN THE RANGE OF 20 TO 30 KT...WITH HIGHEST WINDS OFF
THE CLIMATOLOGICALLY PREVALENT COLOMBIAN COAST. THESE CONDITIONS
ARE EXPECTED TO PERSIST THROUGH EARLY MONDAY OF NEXT WEEK AS A
COLD FRONT AND FRONTAL TROUGH ENTER THE SW NORTH ATLC...
RELAXING THE PRESSURE GRADIENT.

ATLANTIC OCEAN...
UPPER LEVEL WESTERLIES PREVAIL ACROSS MOST OF THE SW N ATLC W OF
56W...WHILE WATER VAPOR IMAGERY SHOWS A MIDDLE TO UPPER LEVEL
SHORTWAVE TROUGH PROGRESSING NE OF THE DISCUSSION AREA OVER THE
W ATLC WITH AXIS FROM NEAR BERMUDA SW TO NEAR 27N72W...AND
SUPPORTING A DYING STATIONARY FRONT FROM 31N66W TO THE CENTRAL
BAHAMAS NEAR 24N76W. SYNOPTIC LIFT AHEAD OF THE SHORTWAVE IS
PRODUCING SCATTERED MODERATE ISOLATED STRONG CONVECTION WITHIN
150 NM SE OF FRONT. WEAK LOW TO MID LEVEL TROUGHING SE OF THE
FRONT ALONG ABOUT 66W/67W WAS PROMOTING SCATTERED SHOWERS AND
ISOLATED TSTMS OVER THE OPEN WATERS BETWEEN 22N AND 27W. TO THE
NW OF THE FRONT...A 1022 MB HIGH EARLIER TODAY HAS COLLAPSED
WHILE GENERALLY LIGHT ANTICYCLONIC FLOW PERSISTS NW OF THE
FRONT. AS THE UPPER SUPPORT LIFTS NE DURING THE NEXT 24
HOURS...THE FRONT WILL DRIFT NW AND DISSIPATE...WHILE THE GFS
SHOWS A NEW CONVERGENCE BOUNDARY DEVELOPING SAT FROM NEAR
BERMUDA TO THE SE BAHAMAS NEAR 23N75W...WITH SCATTERED MODERATE
CONVECTION EXPECTED ALONG AND SE OF THE NEW BOUNDARY. THE
REMAINDER OF THE CENTRAL AND EASTERN ATLC IS UNDER THE INFLUENCE
OF AN EXPANSIVE AND RELATIVELY STRONG 1039 MB HIGH CENTERED EAST
OF THE AZORES NEAR 38N20W. THE INFLUENCE OF THE RIDGE EXPANDS
SOUTHWARD TO 10N AND SW FROM THE HIGH TO 29N66W. WITH SUCH A
STRONG HIGH PRESSURE SYSTEM IN PLACE...A STRONG PRESSURE
GRADIENT EXISTS WITH GENERALLY MODERATE TO STRONG E-NE TRADES
PREVAILING E OF 60W. EARLY MORNING ASCAT PASSES FROM
METEO-FRANCE METAREA II HIGH SEAS FORECASTS INDICATING POSSIBLE
INTERMEDIATE GALE FORCE NE WINDS IN THE AREAS OF CAPE VERDE...
CAP BLANC...AND CAP TIMIRIS LOCATED OFF THE W AFRICAN COAST FROM
15N-25N E OF 22W.

ALOFT E OF 56W...A VIGOROUS MIDDLE TO UPPER LEVEL CYCLONE WAS
CUT OFF FROM THE MEAN FLOW...CENTERED NEAR 17N40W WITH TROUGH
EXTENDING SW TO NEAR 06N44W. STRONG LOW LEVEL FLOW INDUCED BY
THE PRESSURE GRADIENT COUPLED WITH MID LEVEL SWLY FLOW OCCURRING
E THROUGH SE OF THIS CYCLONE CONTINUES TO YIELD WIDESPREAD
CONVECTION N OF THE ITCZ TO NEAR 14N ACROSS THE ERN ATLC BETWEEN
40W AND THE W AFRICAN COAST ALONG 11N. THE CYCLONE WILL SLOWLY
WEAKEN AND BECOME ELONGATED OVER THE NEXT FEW DAYS...WHILE THE
REGION TO ITS SE REMAINS ACTIVE CONVECTIVELY. LOOK FOR THE FRESH
TO STRONG TRADEWINDS TO PERSIST ACROSS THE TROPICAL ATLC THROUGH
SUN BEFORE THE GRADIENT BEGINS TO WEAKEN LATE SUN INTO MON.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
STRIPLING





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