[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 152349
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT MON SEP 15 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.

...SPECIAL FEATURES...
NONE.

...TROPICAL WAVES...
A LOW AMPLITUDE TROPICAL WAVE IS ALONG 32W/33W S OF 13N MOVING W
NEAR 10 KT. SCATTERED SHOWERS ARE WITHIN 120 NM EITHER SIDE OF
THE WAVE AXIS.

A TROPICAL WAVE IS ALONG 56W/57W SOUTH OF 20N WITH A 1012 MB LOW
ANALYZED ALONG THE WAVE AXIS NEAR 19N56W MOVING W 10-15 KT. THE
WAVE IS EMBEDDED WITHIN A BROAD AREA OF DEEP LAYERED MOISTURE AS
INDICATED BY MIMIC-TPW ANIMATION. 850 MB DERIVED VORTICITY ALSO
SUPPORTS THE POSITION OF THE WAVE/LOW. SCATTERED MODERATE
CONVECTION IS E OF THE WAVE AXIS FROM 14N-17N BETWEEN 50W-54W.
A CLUSTER OF MODERATE CONVECTION IS WITHIN 85 NM NE QUADRANT OF
LOW CENTER. UPPER-LEVEL WINDS ARE UNFAVORABLE FOR DEVELOPMENT...
AND TROPICAL CYCLONE FORMATION IS NOT EXPECTED IN THIS AREA.

A TROPICAL WAVE IS ALONG 73W/74W S OF 20N MOVING W 10-15 KT.
THIS WAVE IS WELL DEPICTED IN THE MOISTURE PRODUCT...AND
SATELLITE DERIVED WINDS.  THIS FEATURE IS ENHANCING CONVECTION
OVER HISPANIOLA AND NEAR THE COLOMBIA/VENEZUELA BORDER...
INCLUDING ALSO THE LAKE MARACAIBO AREA.

AN ACTIVE TROPICAL WAVE IS ALONG 84W S OF 20N MOVING W NEAR 10
KT. A LARGE AREA OF MODERATE TO STRONG CONVECTION IS ASSOCIATED
WITH THE WAVE COVERING FROM 13.5N-18N BETWEEN 81W-85W. THIS
SHOWER/TSTM ACTIVITY IS AFFECTING THE E PORTION OF HONDURAS AND
THE NE PART OF NICARAGUA. A WEAK LOW PRES MAY FORM ON THE WAVE
AS IT CROSSES THE COAST OF HONDURAS AND NICARAGUA ON TUE...AND
POSSIBLY LINGER AS IT DRIFTS NW ALONG THE COAST THROUGH SAT. A
DIFFLUENT PATTERN ALOFT IS ENHANCING THIS CONVECTIVE ACTIVITY.

...THE ITCZ...
ITCZ AXIS IS ANALYZED ALONG 11N15W 10N23W 9N31W 8N40W 10N54W.
BESIDES THE CONVECTION MENTIONED IN THE TROPICAL WAVE SECTION...
A LARGE CLUSTER OF MODERATE TO STRONG CONVECTION IS APPROACHING
THE WEST COAST OF AFRICA LIKELY ASSOCIATED WITH THE TROPICAL
WAVE. SCATTERED MODERATE CONVECTION IS FROM 5N-12N BETWEEN
45W-55W.

...DISCUSSION...

GULF OF MEXICO...
AN EARLY SEASON COLD FRONT EXTENDS ACROSS THE REGION FROM THE
FLORIDA PANHANDLE TO A DEVELOPING 1015 MB LOW LOCATED NEAR
26N96W. THEN...THE FRONTAL SYSTEM CONTINUES SW ENTERING NE
MEXICO NEAR 23.5N98W. AT THIS POINT...THE FRONT STRETCHES OVER N
MEXICO AS A STATIONARY FRONT. TEMPERATURES ARE FALLING BEHIND
THE FRONT WITH NLY WINDS OF 20 TO 25 KT ARE BLOWING ACROSS THE
NW CORNER OF THE GULF. THIS LOW IS FORECAST BY THE COMPUTER
MODELS TO MOVE SLOWLY NE LINGERING OVER THE NW QUADRANT OF THE
GULF TUE AND WED. AS A RESULT...NLY WINDS IN THE 15-20 KT RANGE
WILL PERSIST OVER THE FAR WEST GULF INCLUDING THE WESTERN
PORTION OF THE BAY OF CAMPECHE. ELSEWHERE...A WEAK SURFACE RIDGE
DOMINATES WITH A 1016 MB HIGH NEAR 27N84W AT 2100 UTC. LATEST
VIS SATELLITE IMAGERY FOR THE DAY SHOWS THE CLOUD PATTERN
EXHIBITING CYCLONIC CIRCULATION DUE TO THE PRESENCE OF THE LOW
OVER THE NW GULF WHILE DOPPLER RADAR DEPICTS SCATTERED SHOWERS
AND TSTMS NEAR THE LOW CENTER. ALOFT...AN UPPER LEVEL TROUGH
EXTENDS FROM THE FLORIDA PANHANDLE TO THE BAY OF CAMPECHE WITH
AN EMBEDDED LOW NEAR 25N90W. THIS FEATURE DOMINATES MOST OF THE
GULF REGION. SWLY FLOW ON THE EASTERN SIDE OF THE LOW/TROUGH IS
HELPING TO INDUCE SOME SHOWER/TSTMS ACTIVITY OVER THE YUCATAN
PENINSULA. A DEEP LAYERED TROUGH OVER THE EAST-CENTRAL CONUS
SUPPORTS THE AFOREMENTIONED FRONTAL ZONE.

CARIBBEAN SEA...
AS IS NORMAL FOR THIS TIME OF THE YEAR...A COUPLE OF TROPICAL
WAVES ARE OVER THE CARIBBEAN SEA GENERATING SHOWER/TSTM
ACTIVITY. SEE TROPICAL WAVE SECTION FOR DETAILS. TRADE WINDS OF
15-20 KT ARE NOTED OVER THE CENTRAL AND EASTERN CARIBBEAN. AN
UPPER-LEVEL HIGH CENTERED NEAR CABO GRACIAS A DIOS NICARAGUA IS
SUPPORTING THE DEVELOPMENT OF SHOWERS AND TSTMS ASSOCIATED WITH
THE TROPICAL WAVE ALONG 84W. AN UPPER-LEVEL LOW IS SPINNING
BETWEEN THE NORTHERN LEEWARD ISLANDS AND THE VIRGIN ISLANDS. THE
CYCLONIC FLOW COVERS THE EASTERN CARIBBEAN. UPPER DIFFLUENCE
BETWEEN THESE UPPER-LEVEL FEATURES IS SUPPORTING CONVECTION OVER
PUERTO RICO AND HISPANIOLA WHILE ISOLATED TO SCATTERED SHOWERS
ARE SEEN OVER THE LEEWARD ISLANDS.

ATLANTIC OCEAN...
A WEAK PRES GRADIENT DOMINATES THE W ATLC DUE TO THE PRESENCE OF
A SFC TROUGH EXTENDING FROM A 1011 MB SFC LOW LOCATED NEAR
31N63W TO 26N70W. A NARROW BAND OF MODERATE CONVECTION IS JUST
AHEAD OF THE TROUGH AXIS. THE REMAINDER OF THE FORECAST AREA IS
UNDER THE INFLUENCE OF A RIDGE ANCHORED ON A HIGH NEAR THE
AZORES. A PAIR OF TROPICAL WAVES ARE OVER THE TROPICAL ATLANTIC.
THE WESTERNMOST IS APPROACHING THE LESSER ANTILLES. THE NORTHERN
PART OF THIS WAVE WHERE THERE IS A SFC LOW IS FORECAST TO MOVE
MAINLY NORTH WHILE MOISTURE ASSOCIATED WITH THE SOUTHERN PORTION
OF THE WAVE WILL REACH THE WINDWARD ISLAND EARLY WED. IN THE
UPPER LEVELS...RIDGING IS OVER THE WESTERN ATLANTIC REACHING THE
BAHAMAS. ELONGATED LOW PRESSURE EXTENDS FROM 24N60W TO THE NE
CARIBBEAN. AN UPPER-LEVEL TROUGH EXTENDS MAINLY EAST TO WEST
ALONG 26N FROM AN UPPER-LEVEL LOW SITUATED NEAR 31N20W TO
ANOTHER AND WEAKER ONE LOCATED NEAR 24N44W. SOUTH OF THIS
TROUGH...A LARGE UPPER LEVEL HIGH CENTERED WEST OF THE CAPE
VERDE ISLANDS NEAR 16N28W COVERS MOST OF THE TROPICAL ATLC. SLY
WINDS ON THE WESTERN PERIPHERY OF THIS HIGH IS LIMITING THE
DEVELOPMENT OF THE SFC LOW LOCATED NEAR 19N56W...BUT IS
ENHANCING CONVECTION ALONG THE ITCZ WEST OF 45W.

$$
GR


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