000
AXNT20 KNHC 212353
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE OCT 21 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.

...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 22W S OF 15N MOVING W NEAR 10 KT. THIS
WAVE HAS WEAKENED SINCE YESTERDAY AND NOW MOST OF THE CONVECTIVE
ACTIVITY IS CONFINED TO THE ITCZ. THIS FEATURE STILL SHOWS UP ON
THE TOTAL PRECIPITABLE WATER AND 850 MB RELATIVE VORTICITY
PRODUCTS FROM CIMSS.

A TROPICAL WAVE IS ALONG 50W S OF 22N MOVING W 10-15 KT. THE
SSMI-TPW PRODUCT FROM CIMSS INDICATES A NORTHWARD SURGE OF
MOISTURE ALONG THE WAVE AXIS. THE WAVE IS INTERACTING WITH A
SHARP UPPER-LEVEL TROUGH WITH AXIS ALONG 50W/51W. UPPER
DIFFLUENCE AHEAD OF THIS TROUGH IS ENHANCING CONVECTION NEAR THE
NORTHERN END OF THE WAVE AXIS. SATELLITE IMAGERY REVEALS A LARGE
AREA OF MODERATE TO ISOLATED STRONG CONVECTION EXTENDING NWD
FROM 18N-25N BETWEEN 47W-50W.

A TROPICAL WAVE IS ALONG 75W S OF 15N MOVING W 10-15 KT. THE
WAVE IS LOCATED WITHIN STRONG EASTERLY SURFACE FLOW ACROSS THE
CARIBBEAN AND THIS EVENING IS ENHANCING CONVECTION OVER NORTHERN
COLOMBIA WHERE A CLUSTER OF MODERATE TO ISOLATED CONVECTION IS
SEEN. LATEST VIS IMAGERY FOR THE DAY SHOWED A SWIRL OF LOW
CLOUDS JUST AHEAD OF THE WAVE AXIS NEAR 12N76W.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 9N13W 8N20W 7N30W 10N48W 9N61W.
SCATTERED MODERATE CONVECTION IS FROM 5N-10N BETWEEN 41W-50W.
SIMILAR CONVECTION IS NEAR 5N18W.

...DISCUSSION...

GULF OF MEXICO...
A BROAD UPPER-LEVEL HIGH CENTERED IN THE CENTRAL CARIBBEAN SEA
EXTENDS WEAK RIDGING ACROSS THE ENTIRE GULF PRODUCING A W TO SW
UPPER LEVEL FLOW. MODERATE TO STRONG SUBSIDENCE/DRY AIR IS NOTED
OVER MUCH OF THE GULF. AT THE SURFACE...A SFC TROUGH HAS
DEVELOPED OVER THE WESTERN GULF ALONG 93W FROM 21N-26N. WEAK
CYCLONIC TURNING IS OBSERVED ALONG THE TROUGH AXIS NEAR 22N.
ISOLATED SHOWERS ARE ASSOCIATED WITH THIS FEATURE. A 1025 MB
HIGH PRESSURE CENTERED OVER NORTHERN ALABAMA EXTENDS A RIDGE
ACROSS THE NRN GULF WATERS N OF 25N. THIS RIDGE IS FORECAST TO
MOVE EWD AS A COLD FRONT MOVES OFF THE TEXAS COAST LATE WED.
MODERATE TO STRONG NLY WINDS ARE EXPECTED IN THE WAKE OF THE
FRONT. WINDS ARE ALSO EXPECTED TO INCREASE ACROSS THE NE CORNER
OF THE GULF BY THU DUE TO A TIGHT PRES GRADIENT BETWEEN A STRONG
SURFACE HIGH ALONG THE EASTERN SEABOARD AND A LOW PRES OVER THE
CENTRAL GULF.

CARIBBEAN SEA...
A LARGE AREA OF DISTURBED WEATHER REMAINS OVER THE NORTHWESTERN
CARIBBEAN SEA. A SFC TROUGH IS ANALYZED ON THE 1800 UTC SFC MAP
ALONG 86W SOUTH OF 21N. PRESSURES HAVE RISEN IN THIS AREA AND
THE SYSTEM REMAINS DISORGANIZED. SIGNIFICANT DEVELOPMENT APPEARS
UNLIKELY. THE GFS COMPUTER MODEL MOVES THIS AREA OF LOW PRES
NORTH AHEAD OF THE COLD FRONT FORECAST TO ENTER THE GULF OF
MEXICO LATE WED. LOCALLY HEAVY RAINS ARE STILL POSSIBLE OVER
PORTIONS OF HONDURAS...GUATEMALA...BELIZE...AND THE YUCATAN
PENINSULA. SCATTERED MODERATE CONVECTION IS MAINLY EAST OF THE
TROUGH AXIS FROM 13N-21N BETWEEN 80W-86W. SIMILAR CONVECTION IS
NOTED OVER PARTS OF HONDURAS AND NICARAGUA. UPPER-LEVEL
DIFFLUENCE ASSOCIATED WITH AN UPPER-LEVEL HIGH LOCATED SOUTH OF
HISPANIOLA NEAR 15N72W WHICH DOMINATES THE ENTIRE CARIBBEAN SEA
IS HELPING TO INDUCE THE CONVECTIVE ACTIVITY OVER THE WESTERN
CARIBBEAN AND CENTRAL AMERICA. ANOTHER SURFACE TROUGH EXTENDS
ACROSS CENTRAL CUBA INTO THE BAHAMAS THEN CONTINUES NE AS A
FRONTAL BOUNDARY OVER THE ATLANTIC OCEAN. MODERATE TRADE WINDS
OF 15 TO 20 KT ARE BLOWING ACROSS THE BASIN. A FEW SHOWERS ARE
MOVING ACROSS THE SRN WINDWARD ISLANDS AND THE FAR SE CARIBBEAN.
THIS ACTIVITY APPEARS TO BE ASSOCIATED WITH THE TAIL END OF AN
UPPER-LEVEL TROUGH LOCATED OVER THE CENTRAL ATLC ALONG 50W/51W.
LOW-TOPPED SHOWERS ARE MOVING WWD ACROSS THE E AND CENTRAL
CARIBBEAN UNDER AN ELY WIND FLOW. SCATTERED SHOWERS AND TSTMS
ARE AFFECTING COSTA RICA AND PARTS OF PANAMA LIKELY ASSOCIATED
WITH THE CLOSE PROXIMITY OF THE ITCZ.

ATLANTIC OCEAN...
A DEEP LAYERED TROUGH IS OVER THE W ATLC. THE ATTENDANT COLD
FRONT ENTERS THE AREA NEAR 31N55W...TURNING STATIONARY NEAR
22N66W...AND EXTENDS ACROSS THE SE BAHAMAS INTO CENTRAL CUBA.
A BAND OF MULTILAYERED CLOUDS WITH ISOLATED SHOWERS IS RELATED
TO THIS FRONT OVER THE ATLC. SCATTERED SHOWERS ARE OVER THE
CENTRAL BAHAMAS AND WESTERN CUBA NEAR THE FRONTAL BOUNDARY/SFC
TROUGH. MODERATE TO  STRONG SUBSIDENCE IS IN PLACE ACROSS THE W
ATLC N OF 26N AND W OF THE COLD FRONT. A BAND OF TRANSVERSE HIGH
CLOUDS ASSOCIATED WITH STRONG UPPER-LEVEL WLY WINDS EXTENDS FROM
THE NE PORTION OF THE YUCATAN PENINSULA ACROSS WESTERN CUBA AND
THE CENTRAL BAHAMAS INTO THE ATLANTIC OCEAN. PATCHES OF
LOW-LEVEL CLOUDS AND MODERATE TRADE WINDS ARE SEEN OVER THE
EASTERN ATLC THANKS TO A 1024 MB SFC HIGH LOCATED NORTH OF AREA
NEAR 34N36W. A SHARP UPPER-LEVEL TROUGH WITH AXIS ALONG 50W/51W
AND AN AMPLIFIED UPPER-LEVEL RIDGE WITH AXIS ALONG 40W CONTINUES
TO FUNNEL DEEP-LAYERED TROPICAL MOISTURE NORTHWARD INTO THE
CENTRAL ATLC. ANOTHER UPPER-LEVEL TROUGH HAS ITS AXIS JUST WEST
OF THE THE CANARY AND CAPE VERDE ISLANDS. THE BASE OF THIS
TROUGH REACHES 10N32W.

$$
GR