[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 202347
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT MON OCT 20 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 EMERGED OFF THE WEST COAST OF AFRICA THIS
MORNING. ITS AXIS IS CURRENTLY ALONG 20W SOUTH OF 13N MOVING
WEST AT 10-15 KT. LATEST VIS IMAGERY FOR THE DAY REVEALS A
BROAD CYCLONIC CIRCULATION AND A DISTINCT INVERTED-V CLOUD
SIGNATURE AROUND THE WAVE AXIS. THIS FEATURE SHOWS UP VERY WELL
ON THE SSMI-TPW PRODUCT WHERE A BULGE OF MOISTURE IS SEEN.
SCATTERED MODERATE CONVECTION IS WITHIN 200 NM BEHIND THE WAVE
AXIS FROM 11N-14N AND NEAR 8N24W.

A TROPICAL WAVE IS ALONG 45W S OF 18N MOVING W NEAR 10 KT. THE
TPW PRODUCT FROM CIMSS INDICATES A NORTH-SOUTH MOISTURE MAXIMUM
ALONG THE WAVE AXIS. CONVECTION ASSOCIATED WITH THIS WAVE IS
RAPIDLY BEING DRAWN NORTHWARD BY AN UPPER-LEVEL LOW LOCATED WEST
OF THE WAVE AXIS NEAR 21N51W.

A LOW AMPLITUDE TROPICAL WAVE IN THE CENTRAL CARIBBEAN ALONG 71W
SOUTH OF 15N MOVING WEST 10-15 KT. THE WAVE IS GENERATING
SCATTERED MODERATE CONVECTION OVER WESTERN VENEZUELA INCLUDING
THE LAKE MARACAIBO AREA. 850 MB RELATIVE VORTICITY AND THE TPW
PRODUCTS FROM CIMSS SUPPORT THE LOCATION OF THE WAVE LINE.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 7N12W 8N22W 4N33W 9N46W TO 8N61W. IN
ADDITION TO CONVECTION ASSOCIATED WITH TROPICAL WAVES...
SCATTERED MODERATE CONVECTION IS WITHIN 70-90 NM S OF THE AXIS
AND WITHIN 45 NM N OF AXIS BETWEEN 24W-30W. SCATTERED MODERATE
TO ISOLATED STRONG CONVECTION IS FROM 10-14N BETWEEN 48W-58W. A
DIFFLUENT PATTERN ALOFT IS HELPING TO INDUCE THIS AREA OF
CONVECTION.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER-LEVEL TROUGH EXTENDING OVER THE SE PORTION OF THE GULF
AND THE EASTERN BAY OF CAMPECHE IS PRODUCING MODERATE TO STRONG
SUBSIDENCE ACROSS THE ENTIRE GULF REGION. THIS TROUGH IS
FORECAST TO DISSIPATE IN ABOUT 24-36 HOURS. AS A RESULT...A
ZONAL FLOW WILL DOMINATE THE GULF BY MIDWEEK. AT THE SURFACE...
HIGH PRES CENTERED OVER THE SE CONUS EXTENDS A RIDGE ACROSS THE
AREA WITH A MOSTLY DRY AND STABLE ATMOSPHERE. E TO NE WINDS OF
10-15 KT ARE FOUND ACROSS MUCH OF THE REGION. WINDS INCREASE TO
20 KT OVER THE SE PORTION OF THE GULF DUE TO THE PRESENCE OF A
FRONTAL BOUNDARY OVER THE FAR NW CARIBBEAN AND A SFC LOW OVER
THE GULF OF HONDURAS. PATCHY CLOUDS WITH ISOLATED SHOWERS ARE
OBSERVED ON SATELLITE IMAGERY PARTICULARLY SOUTH OF 24N BETWEEN
85W-90W. EXPECT THE RIDGE ACROSS THE GULF TO WEAKEN IN ADVANCE
OF A WEAK FRONT FORECAST TO MOVE OUT OF THE TEXAS COAST LATE
WED.

CARIBBEAN SEA...
AS OF 2100 UTC...A 1010 MB SURFACE LOW PERSISTS OVER THE GULF OF
HONDURAS NEAR 16N87W. THIS SYSTEM IS PRODUCING DISORGANIZED
SHOWERS AND THUNDERSTORMS OVER A LARGE PORTION OF THE NW
CARIBBEAN SEA...BUT MAINLY FROM 15N-20N BETWEEN 78W-82W. A
CLUSTER OF MODERATE CONVECTION IS WITHIN 75 NM JUST NORTH OF THE
LOW CENTER. SURFACE PRESSURES ARE RISING IN THIS AREA AND
DEVELOPMENT...IF ANY...WILL BE SLOW TO OCCUR. LOCALLY HEAVY
RAINS ARE POSSIBLE OVER PORTIONS OF HONDURAS...GUATEMALA...
BELIZE...AND THE YUCATAN PENINSULA DURING THE 24-48 HOURS. AN
UPPER-LEVEL HIGH LOCATED SOUTH OF HISPANIOLA DOMINATES MOST OF
THE CARIBBEAN SEA. UPPER DIFFLUENCE BETWEEN THIS HIGH AND AN
UPPER-LEVEL TROUGH OVER THE GULF OF MEXICO IS ENHANCING
CONVECTION ASSOCIATED WITH THE AFOREMENTIONED SFC LOW.
ACCORDING TO THE GFS MODEL...THIS LOW WILL REMAIN STATIONARY IN
THE GULF OF HONDURAS NEAR THE BELIZE COAST DURING THE NEXT
COUPLE OF DAYS...THEN WILL MOVE ACROSS THE YUCATAN PENINSULA
INTO THE SOUTH-CENTRAL GULF OF MEXICO BY THU. PRES GRADIENT
BETWEEN THIS SFC LOW AND HIGH PRES OVER THE GULF OF MEXICO IS
PRODUCING MODERATE TO STRONG ELY WINDS ACROSS THE FAR NW
CARIBBEAN JUST SOUTH OF CUBA AND ALSO SOUTH OF A STATIONARY
FRONT THAT EXTENDS FROM CENTRAL CUBA TO THE NE PORTION OF THE
YUCATAN PENINSULA. AN EARLIER QSCAT PASS SHOWED UNCONTAMINATED
WIND BARS OF 15 TO 20 KT. IN ADDITION...NOAA BUOY 42056 IN THE
NW CARIBBEAN IS ALSO REPORTING ELY WINDS OF 20 KT. MODERATE
TRADE WINDS ARE BLOWING ACROSS THE EAST AND CENTRAL CARIBBEAN
SEA. EXPECT THE FRONTAL BOUNDARY TO DISSIPATE IN ABOUT 12-24
HOURS.

ATLANTIC OCEAN...
A DEEP LAYERED TROUGH OVER THE W ATLC SUPPORTS A COLD FRONT THAT
ENTERS THE AREA NEAR 31N61W THEN CONTINUES SW THROUGH THE
CENTRAL BAHAMAS TO NEAR 22N77W. AT THIS POINT...IT BECOMES
STATIONARY CROSSING CENTRAL CUBA AND THE FAR NW CARIBBEAN INTO
THE NE PORTION OF THE YUCATAN PENINSULA. A BAND OF MULTILAYERED
CLOUDS WITH EMBEDDED SHOWERS IS WITHIN 120 NM AHEAD OF FRONT.
TO THE EAST...A 1026 MB HIGH IS SITUATED NEAR 32N36W AND EXTENDS
A RIDGE OVER THE REMAINDER OF THE FORECAST AREA. A LARGE
UPPER-LEVEL LOW NEAR 21N51W AND AN UPPER-LEVEL HIGH NEAR 19N38W
CONTINUE TO FUNNEL DEEP-LAYER TROPICAL MOISTURE NORTHWARD INTO
THE CENTRAL ATLC. UPPER-LEVEL DIFFLUENCE BETWEEN THIS LOW AND
THE UPPER-LEVEL HIGH LOCATED OVER THE CARIBBEAN SEA IS ENHANCING
CONVECTION ALONG THE ITCZ EAST OF THE WINDWARD ISLANDS TO 48W.
ANOTHER UPPER-LEVEL TROUGH EXTENDS BETWEEN THE CANARY/CAPE VERDE
ISLANDS AND THE WEST COAST OF AFRICA.

$$
GR







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