[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 121801
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST MON NOV 12 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.

...TROPICAL WAVES...
TROPICAL WAVE IS ALONG 67W/68W S OF 16N MOVING W NEAR 20 KT.
VIS SATELLITE IMAGERY AND THE SAHARAN AIR LAYER PRODUCT FROM
CIMMS ARE STILL SHOWING A LARGE SURGE OF AFRICAN DUST JUST
BEHIND THE WAVE AXIS. MOST OF THE LESSER ANTILLES HAVE REPORTED
HAZE SINCE YESTERDAY. THE WAVE IS GENERATING SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS S OF 16N BETWEEN 66W-72W...INCLUDING
THE ABC ISLANDS.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 8N13W 6N25W 7N40W 7N50W 5N57W.
CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION COVERS
THE AREA FROM 4N-10N E OF 21W. SIMILAR CONVECTION IS WITHIN 200
NM N OF AXIS BETWEEN 25W-30W...AND WITHIN 90/120 NM EITHER SIDE
OF AXIS FROM 36W-44W.

DISCUSSION...

GULF OF MEXICO...
THE GULF CONTINUES UNDER THE INFLUENCE OF A SURFACE RIDGE
ANCHORED ON A HIGH CENTERED OVER THE CAROLINAS. THIS FEATURE IS
PRODUCING MOSTLY FAIR WEATHER AND LIGHT TO MODERATE WINDS OVER
THE REGION. A LINE OF MAINLY LOW/MID CLOUDS WITH EMBEDDED
SHOWERS HAS FORMED OVER THE WESTERN GULF ALONG 94W/95W
ASSOCIATED WITH THE SE RETURN FLOW ON THE WESTERN SIDE OF THE
RIDGE. SFC OBSERVATIONS FROM 1500 UTC AND AN EARLIER ASCAT PASS
INDICATED E TO SE WINDS UP TO 20 KT OVER THE SW PORTION OF THE
GULF. ALOFT...BROAD UPPER RIDGE EXTENDS FROM THE W CARIBBEAN
ACROSS THE YUCATAN PENINSULA/CHANNEL INTO THE GULF WHERE UPPER
LEVEL WINDS ARE NEARLY ZONAL. MID/UPPER DRY AIR...RESULTING IN
MODERATE TO STRONG SUBSIDENCE ALSO COVERS THE AREA LIMITING THE
DEVELOPMENT OF DEEP CONVECTION. NO MAJOR CHANGES IN THE WEATHER
PATTERN ARE EXPECTED AS HIGH PRESSURE OVER THE CAROLINAS SHIFTS
SOUTH OVER THE NORTHERN CENTRAL GULF BY MID WEEK. LOOKING
AHEAD...THE NEXT COLD FRONT IS FORECAST TO MOVE ACROSS THE GULF
ON THURSDAY WITH AN INCREASE IN WINDS AND SEAS.

CARIBBEAN SEA...
ATTENTION REMAINS FOCUSED ON AN ELONGATED AREA OF CLOUDINESS...
SHOWERS...AND THUNDERSTORMS COVERING PARTS OF THE WEST AND SW
CARIBBEAN. THIS ACTIVITY IS ASSOCIATED WITH A 1008 MB LOW
PRESSURE LOCATED NEAR THE EAST COAST OF SOUTHERN NICARAGUA. THIS
SYSTEM IS POORLY ORGANIZED AND TROPICAL CYCLONE DEVELOPMENT IS
NOT EXPECTED. A SWIRL OF LOW LEVEL CLOUDS DEFINES THE LOW PRES
WHILE MOST OF THE CONVECTIVE ACTIVITY IS WITHIN 120 NM NORTH OF
CENTER. THE MOST SIGNIFICANT IMPACT WITH THIS SYSTEM REMAINS
THE POTENTIAL FOR LOCALLY HEAVY RAIN OVER PORTIONS OF COSTA
RICA...NICARAGUA AND HONDURAS DURING THE NEXT COUPLE OF DAYS.
VIS SATELLITE IMAGERY INDICATES THAT PART OF THE SHOWER/TSTM
ACTIVITY ASSOCIATED WITH THIS SYSTEM IS ALREADY AFFECTING THESE
COUNTRIES. A SFC TROUGH EXTENDS FROM THIS LOW TO NEAR THE CAYMAN
ISLANDS. CLUSTERS OF MODERATE TO STRONG CONVECTION ARE MAINLY ON
THE EAST SIDE OF THE TROUGH FROM 11N-18N WEST OF 77W...WITH
LIGHTNING DATA SUPPORTING SCATTERED TSTMS MAINLY NEAR 13N78W AND
16N80W. CONVECTION HAS ALSO FLARED UP OVER JAMAICA AND COASTAL
WATERS. BROAD UPPER RIDGE EXTENDING ACROSS THE BASIN FROM AN
UPPER HIGH LOCATED JUST EAST OF THE LESSER ANTILLES IS PROVIDING
ENOUGH UPPER LEVEL DIFFLUENCE TO GENERATE ALL THIS CONVECTION.
A NARROW LINE OF SHOWERS WITH EMBEDDED TSTMS EXTENDS FROM PUERTO
RICO NEWD ACROSS THE W/CENTRAL ATLC. THIS LINE MARKS THE LEADING
EDGE OF THE AFRICAN DUST THAT HAS FILTERED IN THE EASTERN
CARIBBEAN...AND ALSO SEPARATES LIGHTER ELY WINDS FROM STRONGER
NE WINDS IN THE RANGE OF 20-25 KT. THE SAN JUAN DOPPLER RADAR
SHOWS SCATTERED TO NUMEROUS SHOWERS AND ISOLATED TSTMS MAINLY
OVER THE SW AND WEST INTERIOR OF PUERTO RICO...CAPABLE OF
PRODUCING LOCALLY HEAVY RAIN. ANOTHER SFC TROUGH...REMNANTS OF
AN OLD FRONTAL BOUNDARY RESIDES OVER NORTHERN HISPANIOLA
GENERATING SCATTERED TO NUMEROUS SHOWERS AND ISOLATED TSTMS. THE
BASE OF AN UPPER-LEVEL TROUGH OVER THE W-CENTRAL ATLC IS
ENHANCING THIS ACTIVITY.

ATLANTIC OCEAN...
BROAD UPPER TROUGH COVERS THE W-CENTRAL ATLC WITH THE BASE OF
THE TROUGH JUST N OF HISPANIOLA. THE ASSOCIATED COLD FRONT CLIPS
THE FORECAST REGION NEAR 31N54W...THEN CONTINUES AS A WEAKENING
SURFACE TROUGH TO THE CENTRAL BAHAMAS INTO THE STRAITS OF
FLORIDA. PATCHES OF LOW/MID CLOUDS WITH ISOLATED SHOWERS ARE
RELATED TO THE TROUGH MAINLY BETWEEN 60W-70W. A JET STREAM
BRANCH WITH CORE WINDS OF 70-85 KT EXTENDS OVER THE W ATLC N OF
27N. ANOTHER SFC TROUGH ENTERS THE AREA NEAR 30N45W THEN
CONTINUES SW TO THE NORTHERN COAST OF HISPANIOLA. A BAND OF
MULTILAYERED CLOUDS WITH EMBEDDED SHOWERS AND ISOLATED
THUNDERSTORMS IS RELATED TO THIS TROUGH. AN UPPER HIGH IS JUST N
OF BARBADOS EXTENDING A RIDGE NE ACROSS THE CENTRAL ATLC TO
BEYOND 32N35W. AN UPPER-LEVEL TROUGH IS OVER THE FAR E ATLC
EXTENDING SW TO A CUT-OFF LOW NEAR 14N41W...THEN CONTINUING TO N
SOUTH-AMERICA JUST OFFSHORE OF FRENCH GUIANA. THE TYPICAL E/W
UPPER RIDGE CROSS THE TROPICAL ATLC E OF 40W IS HELPING TO
INDUCE SHOWERS AND TSTMS ALONG THE ITCZ.

$$
GR






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