[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 140537
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 AM EST SUN DEC 14 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0515 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 8N13W 4N24W 5N40W 7N50W 6N58W. SCATTERED
MODERATE TO STRONG CONVECTION IS WITHIN 120 NM EITHER SIDE OF
THE AXIS BETWEEN 22W-34W. SCATTERED MODERATE CONVECTION IS
WITHIN 150 NM S OF THE AXIS E OF 14W AND WITHIN 180 NM N OF THE
AXIS BETWEEN 46W-49W.

...DISCUSSION...

GULF OF MEXICO...
STRONG W TO NW MID-UPPER FLOW IS SPREADING WIDESPREAD PACIFIC
MOISTURE N OF 24N...BUT EMBEDDED SHOWERS ARE LIKELY ONLY
ISOLATED AT MOST W OF 87W AIDED BY MOIST LOW-LEVEL FLOW. DRIER
AIR IS PRESENT S OF 24N CLOSER TO AN UPPER RIDGE AXIS OVER
CENTRAL AMERICA. IN THE LOWER LEVELS...STRONG HIGH PRES OVER SE
VIRGINIA IS PRODUCING STRONG E WINDS OVER THE E GULF AND SE TO S
WINDS ELSEWHERE...MODIFYING THE COOL AIRMASS THAT WAS IN PLACE
OVER THE PAST COUPLE OF DAYS. THESE WINDS WILL BECOME MORE
UNIFORM S TO SE LATER TODAY AND MON AS THE NEXT COLD FRONT
APPROACHES THE TEXAS COAST.

CARIBBEAN SEA...
AN UPPER HIGH CENTERED OVER CENTRAL AMERICA HAS HELPED SET UP
ZONAL TO NW FLOW AND ABUNDANT DRY SINKING AIR OVER MUCH OF THE
AREA. ONLY AREA OF SIGNIFICANT MOISTURE IS NEAR THE COAST OF
COSTA RICA AND NICARAGUA...LIKELY PRODUCED BY LOW-LEVEL SPEED
CONVERGENCE (EVIDENT IN QSCAT DATA) AND DIFFLUENCE ALOFT NEAR
THE UPPER HIGH CENTER. OTHERWISE...PATCHES OF LOW-LEVEL MOISTURE
WITH EMBEDDED SHOWERS ARE SCATTERED ACROSS THE REMAINDER OF THE
W CARIBBEAN ASSOCIATED WITH THE REMNANTS OF AN OLD FRONTAL
BOUNDARY. LITTLE LARGE SCALE CHANGES ARE EXPECTED OVER THE NEXT
COUPLE OF DAYS.

ATLANTIC OCEAN...
AN UPPER TROUGH ALONG 64W IS FLATTENING SLIGHTLY BUT STILL
PROVIDING SUPPORT FOR A COLD FRONT EXTENDING FROM 31N62W TO
22N72W. THE TIGHT PRES GRADIENT BETWEEN THE FRONT AND A 1033 MB
HIGH OVER SE VIRGINIA IS PRODUCING A LARGE AREA OF 20-30 KT NE
WINDS W OF THE FRONT. UPPER DIFFLUENCE E OF THE UPPER TROUGH
AXIS IS PRODUCING A SWATH OF SCATTERED SHOWERS AND TSTMS N OF
25N BETWEEN 59W-62W.

FARTHER E...AN UPPER LOW AND A HIGHLY DIFFLUENT UPPER PATTERN IS
PRODUCING A LARGE AREA OF SCATTERED SHOWERS AND TSTMS N OF 17N
BETWEEN 39W-52W. SHORTWAVE IR IMAGES AND QSCAT DATA REVEALS AN
ASSOCIATED SFC TROUGH ALONG 55W N OF 25N...BUT NEARLY ALL OF THE
ASSOCIATED WEATHER IS LOCATED IN THE DIFFLUENT ZONE TO ITS E.
THE SFC PRES PATTERN IS VERY TIGHT BETWEEN THE TROUGH AND A 1040
MB HIGH JUST W OF THE AZORES PRODUCING 20-30 KT E WINDS ACROSS
THE SUBTROPICAL ATLC E OF THE TROUGH AXIS.  NWP MODELS CONTINUE
TO SUGGEST POSSIBLE LOW PRES DEVELOPMENT OVER THE NEXT FEW DAYS
OVER THE CENTRAL ATLC...ASSOCIATED WITH THE COMBINED EFFECTS OF
THE DEEP LAYER TROUGHING AND THE TAIL END OF THE WEAKENING
FRONT. IN ANTICIPATION OF THE LOW DEVELOPMENT...A GALE WARNING
IS POSTED FOR AN AREA NW OF THE LOW...DUE TO THE STRONG GRADIENT
BETWEEN IT AND HIGH PRES OVER THE N CENTRAL ATLC. OVER THE FAR
TROPICAL E ATLC...AN UPPER JET ALONG 19N/20N IS ADVECTING
ABUNDANT MID-HIGH LEVEL MOISTURE TO ITS S E OF 40W AND ENHANCING
CONVECTION WITHIN THE ITCZ.

$$
CANGIALOSI





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