[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 200546
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT THU SEP 20 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0515 UTC.

...SPECIAL FEATURE...
A 1007 MB SURFACE LOW PRESSURE AREA ALONG THE COAST OF FLORIDA
NEAR 28N81W AND AN UPPER-LEVEL LOW IN THE EASTERN GULF OF MEXICO
ARE PRODUCING A LARGE AREA OF DISTURBED WEATHER OVER THE WESTERN
ATLANTIC...THE CENTRAL AND NORTHWESTERN BAHAMAS... PORTIONS OF
THE FLORIDA PENINSULA...AND THE EASTERN GULF MEXICO. THE SFC LOW
IS MOVING SLOWLY WESTWARD ACROSS NORTH CENTRAL FLORIDA.
HOWEVER...SATELLITE IMAGES INDICATE THAT THE SHOWER ACTIVITY
REMAINS DISORGANIZED. SURFACE PRESSURES ARE STILL FALLING
SHARPLY AND THE ENVIRONMENT IS GRADUALLY BECOMING FAVORABLE FOR
A SUBTROPICAL OR TROPICAL CYCLONE TO FORM...AS THE SYSTEM MOVES
WESTWARD INTO THE EASTERN GULF OF MEXICO TODAY. SHOWERS AND
SQUALLS ASSOCIATED WITH THIS SYSTEM ARE EXPECTED TO SPREAD OVER
PORTIONS OF FLORIDA DURING THE NEXT DAY OR TWO. THE SURFACE
WINDS IN THE IMMEDIATE VICINITY OF THE LOW ARE NOT VERY
STRONG...MOSTLY 15 KT OR LESS. STRONGER WINDS ARE DISPLACED
FURTHER N OF THE LOW WHERE THE INTERACTION BETWEEN THE LOW
ITSELF...STRONG CONTINENTAL HIGH PRESSURE CENTERED OVER NEW
ENGLAND...AND A SLOW MOVING COASTAL WARM FRONT ARE PRODUCING
20-25 KT NE TO E WINDS OFF THE COAST OF SOUTH CAROLINA AND
GEORGIA. MODERATE N TO NE WINDS OF 20 KT ARE ALSO BLOWING OVER
THE NE CORNER OF THE GULF. ALL INTEREST ALONG THE NORTHERN GULF
OF MEXICO COAST SHOULD MONITOR THE PROGRESS OF THIS WEATHER
DISTURBANCE.

...TROPICAL WAVES...

A NEW TROPICAL WAVE WILL BE ADDED TO THE 0600 UTC ANALYSIS/SFC
MAP ALONG 2OW/21W BASED ON SATELLITE IMAGERY AND THE VERTICAL
SOUNDING FROM DAKAR SENEGAL THAT SHOWED THE PASSAGE OF THE WAVE
YESTERDAY. THE 20/00Z SOUNDING FROM SAL CAPE VERDE ISLANDS IS
SHOWING NE WINDS OF 15 TO 20 KT AT LOW LEVEL INDICATING THE
APPROACH OF THE WAVE. IN ADDITION...850 MB AND 700 MB MODEL
GUIDANCE INDICATE THE WIND SHIFT ASSOCIATED WITH THE WAVE.
ALSO...THE CIMSS VORTICITY PRODUCT PROVIDES SOME SUPPORT FOR THE
WAVE POSITION INDICATED. SCATTERED MODERATE CONVECTION IS WITHIN
150 NM EITHER SIDE OF THE AXIS FROM 11N-15N.

A LOW AMPLITUDE TROPICAL WAVE IS OVER THE ATLC ALONG 32W S OF
15N MOVING W 10-15 KT. THIS WAVE STILL SHOWS UP WELL IN LOW
LEVEL SATELLITE DERIVED WINDS AND VORTICITY...AND THE UW CIMSS
TPW PRODUCTS. SCATTERED MODERATE CONVECTION IS SEEN NEAR THE
INTERSECTION OF THE WAVE AND THE ITCZ.

TROPICAL WAVE IS ALONG 56W/57W S OF 21N MOVING W NEAR 15 KT.
THIS WAVE IS NOT VERY WELL ORGANIZED. ONLY ISOLATED SHOWERS ARE
NEAR THE WAVE AXIS BETWEEN 15N-16N. A CLUSTER OF MODERATE TO
ISOLATED STRONG CONVECTION REMAINS WITHIN 230 NM E OF THE NRN
PORTION OF THE WAVE. THIS ACTIVITY IS BEING ENHANCED BY UPPER
DIFFLUENCE.

TROPICAL WAVE IS OVER THE YUCATAN PENINSULA AND BELIZE ALONG 88W
S OF 21W MOVING W 10-15 KT. SHOWER ACTIVITY REMAINS LIMITED IN
ASSOCIATION WITH THIS WAVE. THE WAVE...COUPLED WITH STRONG UPPER
WLY FLOW IS GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS OVER
THE AREA. THESE WINDS ARE PUSHING THE STORM TOPS TO THE E.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 11N17W 10N25W 7N35W 6N45W 5N56W.
OUTSIDE OF THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVE...
CLUSTERS OF SCATTERED MODERATE TO ISOLATED STRONG CONVECTION ARE
FROM 5N-10N BETWEEN 34W-43W.

DISCUSSION...

GULF OF MEXICO...
ATTENTION REMAINS FOCUSED ON A LARGE AREA OF DISTURBED WEATHER
MOVING SLOWLY WESTWARD ACROSS NORTH-CENTRAL FLORIDA. THIS
ACTIVITY IS ASSOCIATED WITH A WEAK SURFACE LOW PRES AREA AND A
WELL DEFINED UPPER-LEVEL LOW LOCATED OVER THE ERN GULF NEAR
26N84W. A SWATH OF VERY DRY MID TO UPPER AIR CONTINUES TO WRAP
AROUND THE PERIPHERY OF THIS FEATURE THROUGH THE MIDDLE GULF
THEN SE TO FAR WRN CUBA AND NE ACROSS THE FLORIDA PENINSULA.
HOWEVER...SCATTERED SHOWERS AND THUNDERSTORMS ASSOCIATED WITH
THE SYSTEM ARE NOW AFFECTING THE ERN GULF FROM 25N-27N E OF 86W.
A 1007 MB SURFACE LOW NEAR THE COAST OF E FLORIDA IS INTERACTING
WITH THE UPPER LOW. SEE SPECIAL FEATURE SECTION ABOVE FOR MORE
DETAILS. UPPER RIDGING DOMINATES THE FAR NW AND SW PORTIONS OF
THE GULF WHILE ANOTHER UPPER LOW CONTINUES TO MOVE SLOWLY WWD
ACROSS MEXICO. WIDELY SCATTERED SHOWERS ARE OBSERVED OVER THE
WESTERN HALF OF THE GULF. ELSEWHERE AT THE SURFACE RIDGING
DOMINATES N OF 25N FROM THE LARGE FALL-LIKE SURFACE HIGH
EXTENDING FROM NEW ENGLAND JUST TO THE W OF THE APPALACHIAN
MOUNTAINS. THIS IS PRODUCING MODERATE NE TO E WINDS OVER THE N
GULF...WHILE LIGHTER MORE VARIABLE WINDS PERSIST FURTHER S
AROUND TROUGHING.

CARIBBEAN SEA...
TONIGHT...CONVECTION CONTINUES TO FIRE UP OVER PARTS OF
VENEZUELA AND NORTHERN COLOMBIA IN ASSOCIATION WITH THE ITCZ AND
A DIFFLUENT PATTERN ALOFT. SCATTERED MODERATE CONVECTION IS ALSO
SEEN OVER PARTS OF CENTRAL AMERICA AND THE YUCATAN PENINSULA DUE
TO A TROPICAL WAVE LOCATED OVER THE YUCATAN PENINSULA/BELIZE.
THE SURFACE PRES GRADIENT REMAINS FAIRLY RELAXED ACROSS THE
AREA. THIS IS KEEPING THE TRADE WINDS MOSTLY LIGHT...EXCEPT
SLIGHTLY STRONGER NEAR THE COAST OF COLOMBIA. EXTENSIVE WLY FLOW
ALOFT IS OVER THE MAJORITY OF THE BASIN...WITH RIDGING OVER
NORTHERN SOUTH AMERICA AND CENTRAL AMERICA.

ATLANTIC OCEAN...
SHOWERS AND THUNDERSTORM ACTIVITY CONTINUES OVER THE WRN ATLC
AND THE BAHAMAS ASSOCIATED WITH A LARGE AREA OF DISTURBED
WEATHER. SEE SPECIAL FEATURE ABOVE. CLUSTERS OF MODERATE TO
ISOLATED STRONG CONVECTION ARE FOUND OVER THE CENTRAL ATLC FROM
16N-30N BETWEEN 42W-53W...WHICH IS IN A REGION OF PRONOUNCED
UPPER DIFFLUENCE BETWEEN AN UPPER LOW NEAR 31N51W AND AN UPPER
HIGH LOCATED EAST OF THE LESSER ANTILLES NEAR 15N55W. AN UPPER
RIDGE EXTENDS  FROM THIS HIGH N THROUGH THE CENTRAL ATLC ALONG
45W. THE NEXT WEATHER PRODUCER IS THE REMNANTS OF INGRID...
ANALYZED AS A 1012 MB LOW NEAR 22N65W WITH A WEAK SURFACE TROUGH
EXTENDING ALONG 65W FROM 20N-26N. UPPER-LEVEL WINDS ARE NOT
FAVORABLE FOR SIGNIFICANT DEVELOPMENT OF THIS SYSTEM. SCATTERED
SHOWERS AND ISOLATED TSTMS ARE ASSOCIATED WITH THIS FEATURE. A
WEAK 1016 MB SURFACE LOW IS NEAR 30N50W THAT HAS A TRAILING
TROUGH EXTENDING SW TO NEAR 27N52W. ANOTHER UPPER LOW IS OVER
THE E ATLC NEAR 30N25W. AN UPPER TROUGH EXTENDS FROM THIS LOW TO
NEAR 17N37W. RIDGING DOMINATES THE TROPICAL ATLC. THE E ATLC
SURFACE PATTERN CONTINUES TO BE DOMINATED BY RIDGING S OF A 1029
MB HIGH LOCATED N OF THE AZORES. THIS IS PRODUCING MODERATE NE
TRADES E OF 35W...EXCEPT SLIGHTLY STRONG NEAR THE COAST OF NW
AFRICA WHERE THE USUAL STRONGER GRADIENT EXISTS.

$$
GR



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