[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 132343
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST SAT DEC 13 2008

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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...THE ITCZ...
THE ITCZ IS CENTERED ALONG 9N13W 4N30W 5N45W 4N54W. ISOLATED
MODERATE CONVECTION IS WITHIN 120 NM EITHER SIDE OF THE AXIS
BETWEEN 18W-40W. SIMILAR CONVECTION IS ALSO NOTED WITHIN 80 NM N
OF AXIS BETWEEN 42W-47W...AND NEAR 9N48W.
...DISCUSSION...

GULF OF MEXICO...
RELATIVELY COOL AND DRY CONDITIONS ARE PRESENT ACROSS THE GULF
REGION COURTESY OF A 1029 MB HIGH CENTERED OVER THE SE CONUS.
BROKEN COLD AIR STRATOCUMULUS CLOUDS ARE SEEN ON SATELLITE
IMAGERY COVERING MUCH OF THE GULF WATERS PARTICULARLY N OF 23N
AND WEST OF 85W...WITH CLEARING SKIES JUST WEST OF THE FLORIDA
PENINSULA. SURFACE SLY WINDS OF 20 TO 25 KT ARE BLOWING ACROSS
THE WESTERN HALF OF THE GULF IN ADVANCE OF A COLD FRONT FORECAST
TO APPROACH THE TEXAS COAST MON NIGHT. THIS FRONT WILL MOVE
BRIEFLY OVER THE NW GULF WATERS TUE BEFORE GRADUALLY MOVING BACK
INLAND THROUGH MID WEEK. STRONG WESTERLY AND NORTHWESTERLY FLOW
ALOFT IS PRESENT ACROSS THE AREA. THESE WINDS ARE TRANSPORTING
MID/UPPER LEVEL MOISTURE FROM THE EPAC REGION ACROSS N MEXICO
INTO THE GULF WATERS MAINLY N OF 24N. AN UPPER-LEVEL RIDGE
ANCHORED ON A HIGH OVER GUATEMALA DOMINATES THE SOUTH PORTION OF
THE GULF AND SE MEXICO INCLUDING THE YUCATAN PENINSULA. STRONG
UPPER LEVEL SUBSIDENCE AND IMPLIED DRY AIR MASS IS NOTED WITHIN
THIS RIDGE.

CARIBBEAN SEA...
TWO WEAKENING SURFACE FRONTS EXTEND INTO THE CARIBBEAN SEA FROM
THE W ATLC. THE LEAD FRONT IS STATIONARY AND EXTENDS FROM E CUBA
TO E OF NICARAGUA NEAR 12N83W. AN AREA OF SCATTERED MODERATE
CONVECTION IS NEAR THE TAIL END OF THIS FRONT AFFECTING FROM
10N-13N WEST OF 80W. THE SECONDARY FRONT IS OVER WESTERN CUBA. A
RELATIVELY COOLER AND DRIER AIRMASS DOMINATES WEST AND CENTRAL
CUBA...THE NW CARIBBEAN AND NORTHERN CENTRAL AMERICA WHERE
BROKEN LOW TO MID CLOUDS WITH EMBEDDED LIGHT SHOWERS ARE NOTED.
IN ADDITION...NLY WINDS OF 15 TO 25 KT ARE BLOWING W OF THE
STATIONARY FRONT WITH THE STRONGEST WINDS NEAR THE COAST OF
NICARAGUA. EASTERLY WINDS ARE EXPECTED TO INCREASE OVER MOST OF
THE CARIBBEAN SEA AND THE TROPICAL N ATLC SUN AND MON AS HIGH
PRES CURRENTLY OVER THE SE CONUS MOVES NE OVER THE W ATLC. AS IS
TYPICAL FOR THIS TIME OF THE YEAR...FRAGMENTS OF LOW LEVEL
MOISTURE ARE MOVING WWD ACROSS THE E AND CENTRAL CARIBBEAN UNDER
AN ELY WIND FLOW. ALOFT...A RIDGE EXTENDS FROM N COLOMBIA TO
GUATEMALA AND SE MEXICO. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH
THIS UPPER FEATURE IS HELPING TO INDUCE SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS ACROSS THE SW CARIBBEAN INCLUDING ALSO
COSTA RICA AND WESTERN PANAMA.

ATLANTIC OCEAN...
A DEEP LAYERED TROUGH OVER THE WESTERN ATLC SUPPORTS A COLD
FRONT THAT CROSSES JUST E OF BERMUDAS AND ENTERS THE FORECAST
AREA NEAR 31N65W. THIS FRONTAL ZONE CONTINUES SW ACROSS THE SE
BAHAMAS AND EASTERN CUBA WHERE IT BECOMES STATIONARY CONTINUING
OVER THE CARIBBEAN SEA. THE PORTION OF THE FRONT OVER THE
CARIBBEAN SEA IS DISSIPATING...AND AS OF 2100 UTC A SURFACE
TROUGH IS ANALYZED FROM E CUBA TO THE SW CARIBBEAN. A
REINFORCING COLD FRONT...WHICH IS ALSO WEAKENING...IS WITHIN
AROUND 120 NM BEHIND OF THE MAIN FRONT AND LIES OVER THE NW
BAHAMAS AND WESTERN CUBA. A PRE-FRONTAL TROUGH WITH A BAND OF
SCATTERED SHOWERS AND ISOLATED TSTMS REMAINS WITHIN AROUND 70 NM
E OF THE PRIMARY FRONT N OF 23N. SFC HIGH PRES OVER THE SE CONUS
EXTENDS A RIDGE OVER THE W ATLC BEHIND THE AFOREMENTIONED
FRONTS. THIS SYSTEM WILL BE OFFSHORE THE CAROLINAS SUNDAY
MORNING...AND WILL MOVE NE ACROSS THE OPEN OCEAN WATERS OF THE W
AND CENTRAL ATLC SUNDAY THROUGH TUE. NE WINDS OF 20 TO 30 KT
AROUND THIS HIGH ARE BRINGING ABUNDANT CLOUDINESS TO THE STATE
OF FLORIDA AND THE NW BAHAMAS. THE REMAINDER OF THE DISCUSSION
AREA IS UNDER THE INFLUENCE OF A STRONG SFC HIGH PRES SYSTEM
FORECAST TO SHIFT SLIGHTLY EWD APPROACHING THE AZORES DURING THE
NEXT 24 HOURS. SUBSIDENCE AROUND THIS 1040 MB SURFACE HIGH
CENTERED NEAR 37N36W IS GENERALLY SUPPORTING FAIR WEATHER
CONDITIONS ACROSS THE E ATLC. A SURFACE TROUGH HAS DEVELOPED
OVER THE CENTRAL ATLC AND RUNS FROM 28N54W TO 24N52W TO 18N52W.
A LARGE AREA OF SCATTERED MODERATE CONVECTION IS EAST OF THE
TROUGH AXIS COVERING FROM 18N-30N BETWEEN 40W-52W...MORE
CONCENTRATED N OF 25N AND WEST OF 48W. UPPER DIFFLUENCE AHEAD OF
A SHARP UPPER-LEVEL TROUGH LOCATED IN THIS SAME AREA IS
ENHANCING THIS CONVECTIVE ACTIVITY. MOST OF THE COMPUTER MODELS
ANTICIPATE A SURFACE LOW DEVELOPING IN THE VICINITY OF THIS SFC
TROUGH NEAR 26N56W LATE MONDAY NIGHT/EARLY TUE MORNING. WINDS
WILL BE STRONGEST OVER THE W SEMICIRCLE OF THE DEVELOPING LOW
DUE TO THE TIGHT PRES GRADIENT BETWEEN THIS LOW AND THE SFC HIGH
PRES MOVING OFF THE SE CONUS. MAINLY WESTERLY ZONAL FLOW ALOFT
DOMINATES THE DEEP TROPICS...WITH UPPER LEVEL DIFFLUENCE
SUPPORTING THE CONVECTION IN THE VICINITY OF THE ITCZ.

$$
GR





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