[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 170555
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST SAT DEC 17 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0515 UTC.

...ITCZ/MONSOON TROUGH...

THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS FROM 06N11W TO
04N27W TO 06N44W. WIDELY SCATTERED MODERATE CONVECTION IS FROM
04N-08N BETWEEN 24W-40W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL RIDGE REMAINS ANCHORED IN THE WESTERN CARIBBEAN
SEA AND EXTENDS NORTHWARD CONTINUING TO IMPACT MUCH OF THE
EASTERN GULF AND FLORIDA PENINSULA. HOWEVER...A WEAK MIDDLE TO
UPPER LEVEL SHORTWAVE SKIRTS THE CREST OF THE RIDGE MOVING
ACROSS THE SE CONUS AND SUPPORTS A COLD FRONT ANALYZED INTO THE
GULF IN THE VICINITY OF NEW ORLEANS LOUISIANA NEAR 30N90W THEN
SW ALONG 27N95W TO 22N98W. A FEW ISOLATED SHOWERS ARE NOTED ON
MOSAIC DOPPLER RADAR IMAGERY WITHIN 60 NM EITHER SIDE OF THE
FRONT...HOWEVER THE MAIN IMPACT WITH THE FRONT IS INCREASED
NORTHERLY WINDS IN THE RANGE OF 15 TO 20 KT AND MOSTLY OVERCAST
SKIES THIS EVENING. THE FRONT IS FORECAST TO BECOME STATIONARY
THROUGH THE OVERNIGHT HOURS AND DISSIPATE FURTHER OVER THE
WEEKEND. AS THE FRONT DISSIPATES...SURFACE HIGH PRESSURE WILL
BUILD ACROSS THE GULF THROUGH THE REMAINDER OF THE WEEKEND WITH
NORTHEASTERLY WINDS PERSISTING THROUGH SUNDAY NIGHT. BY
MONDAY...SOUTHERLY RETURN FLOW IS EXPECTED TO RE-ESTABLISH OVER
PORTIONS OF THE WESTERN GULF AS A AREA OF LOW PRESSURE DEVELOPS
OVER NORTH TEXAS AND OKLAHOMA.

CARIBBEAN SEA...
AN UPPER LEVEL ANTICYCLONIC CIRCULATION INFLUENCES MUCH OF THE
WESTERN CARIBBEAN CENTERED NEAR 17N80W WITH AXIS EXTENDING
NORTHWARD ALONG 80W. ON THE SOUTHERN PERIPHERY OF THE RIDGE...
S-SE DIFFLUENT FLOW ALOFT CONTINUES TO ENHANCE SCATTERED SHOWERS
AND ISOLATED TSTMS S OF 16N BETWEEN 77W-85W...INCLUDING PORTIONS
OF EASTERN NICARAGUA. MOST OF THIS CONVECTIVE ACTIVITY IS
FOCUSED IN THE VICINITY AND NORTH OF THE MONSOON TROUGH AXIS
EXTENDING FROM THE E PACIFIC ALONG 10N TO NORTHERN COLOMBIA.
OTHERWISE THE REMAINDER OF THE WESTERN CARIBBEAN W OF 70W IS
UNDER STRONG NE TRADES DUE TO AN INCREASED PRESSURE GRADIENT
FROM A HIGH PRESSURE CENTER OVER THE SW NORTH ATLC. FARTHER
EAST...A VERY DRY AND STABLE ATMOSPHERE IS NOTED UNDER NW FLOW
ALOFT ON THE SOUTHWESTERN PERIPHERY OF AN UPPER LEVEL LOW
CENTERED NEAR 26N51W AND ASSOCIATED TROUGHING E OF 70W.
HOWEVER...A PAIR OF WEAK COLD FRONTS EXTEND INTO THE EASTERN
CARIBBEAN...ONE ALONG 13N FROM BARBADOS TO 69W AND A SECONDARY
FRONT TO THE NORTH ALONG 18N FROM 60W TO 66W. LOW-TOPPED WIDELY
SCATTERED SHOWERS ARE OCCURRING WITHIN 90 NM EITHER SIDE OF THE
BOUNDARIES AS THEY CONTINUES TO DRIFT SOUTHWARD AND BECOME MORE
DIFFUSE THROUGH THE OVERNIGHT HOURS. EARLIER ASCAT PASSES AROUND
17/0110 UTC AND 17/0252 UTC INDICATED STRONG NE WINDS NORTHWEST
OF THESE BOUNDARY ACROSS THE EASTERN AND CENTRAL CARIBBEAN
BETWEEN 62W-77W IN THE RANGE OF 20 TO 25 KT. HIGH PRESSURE IS
FORECAST TO REMAIN ANCHORED NE OF THE BAHAMAS THROUGH THE
REMAINDER OF THE WEEKEND MAINTAINING THE AREA OF INCREASED E-NE
TRADES.

ATLANTIC OCEAN...
AN UPPER LEVEL RIDGE ANCHORED IN THE WESTERN CARIBBEAN SEA
CONTINUES TO INFLUENCE THE SW NORTH ATLC W OF 60W. A MOSTLY DRY
AND STABLE AIRMASS IS ASSOCIATED WITH THIS UPPER LEVEL FEATURE
AND CONTINUES TO SUPPORT A 1023 MB SURFACE HIGH CENTERED NEAR
30N72W. MOSTLY NE TO E WINDS ARE OBSERVED W OF 60W WITH A FEW
FAST-MOVING ISOLATED SHOWERS EXPECTED THROUGH THE OVERNIGHT INTO
SATURDAY SW OF A LINE FROM 20N60W TO 30N70W..INCLUDING THE
BAHAMAS...TURKS AND CAICOS...AND AREAS OFFSHORE OF THE FLORIDA
PENINSULA W OF 76W. FARTHER EAST...AN UPPER LEVEL LOW CENTERED
NEAR 26N51W SUPPORTS A COMPLEX AREA OF LOW PRESSURE ACROSS THE
CENTRAL ATLC FOCUSED ON A STATIONARY 1007 MB LOW NEAR 26N51W. A
PAIR OF COLD FRONTS STEM FROM THE LOW...WITH THE PRIMARY FRONT
SLOWLY DISSIPATING FROM 27N47W TO 20N47W TO THE WINDWARD ISLANDS
NEAR 13N61W...AND A SECONDARY COLD FRONT ANALYZED FROM THE LOW
TO 24N50W TO 20N53W TO THE LEEWARD ISLANDS NEAR 18N63W. A PRE-
FRONTAL TROUGH IS LOCATED EAST OF THE PRIMARY FRONT ALONG 13N50W
TO 18N45W TO 23N44W. LOW-LEVEL CONVERGENCE EAST OF THE SURFACE
TROUGH AND FRONT ALONG WITH STRONG MIDDLE TO UPPER LEVEL
DIFFLUENCE IS GENERATING A BROAD AREA OF SCATTERED SHOWERS AND
ISOLATED TSTMS FROM 10N-32N BETWEEN 40W-47W. A FEW ISOLATED
SHOWERS ARE ALSO OCCURRING WITHIN 90 NM EITHER SIDE OF THE
SECONDARY COLD FRONT W OF 57W AND IN THE VICINITY OF THE LOW
CENTER FROM 25N-29N BETWEEN 47W-54W IN ASSOCIATION WITH THE
MIDDLE TO UPPER LEVEL LOW. THE REMAINDER OF THE EASTERN ATLC IS
UNDER THE INFLUENCE OF A SURFACE RIDGE ANCHORED BY A 1034 MB
HIGH CENTERED SE OF THE AZORES NEAR 36N21W. THE RIDGE AXIS
EXTENDS SW FROM THE HIGH TO 18N39W.

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

$$
HUFFMAN




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