[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 210548
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT THU SEP 21 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...

THE LOW PRESSURE AREA...ANALYZED 1005 MB...IN THE GULF OF MEXICO
HAS BEEN MEANDERING DURING THE PAST FEW HOURS AND IS NOW LOCATED
ABOUT 100 NM WEST OF TAMPA FLORIDA. THERE HAS BEEN NO
SIGNIFICANT CHANGE IN ORGANIZATION THIS EVENING BUT BANDS OF
HEAVY SQUALLS ARE FORMING TO THE NORTH OF THE CENTER...AND ARE
ALREADY AFFECTING COASTAL SECTIONS OF THE FLORIDA PANHANDLE. SFC
OBSERVATIONS ARE CURRENTLY REPORTING WINDS MOSTLY IN THE 15-25
KT RANGE...STRONGEST N OF THE CENTER WHERE THE PRESSURE GRADIENT
IS TIGHTENED BETWEEN THE LOW AND RIDGING TO THE NW.
ENVIRONMENTAL CONDITIONS ARE FAVORABLE FOR THIS SYSTEM TO BECOME
A SUBTROPICAL OR TROPICAL CYCLONE AT ANY TIME DURING THE NEXT 24
HOURS AS THE LOW MOVES SLOWLY TOWARD THE WEST-NORTHWEST. ALL
INTERESTS ALONG THE NORTHERN GULF COAST SHOULD CLOSELY MONITOR
THE PROGRESS OF THIS SYSTEM...AND TROPICAL STORM WATCHES AND
WARNINGS COULD BE PROMPTLY REQUIRED FOR PORTIONS OF THIS AREA
TODAY.

...TROPICAL WAVES...

A TROPICAL WAVE IS MOVING ACROSS THE CAPE VERDE ISLANDS WITH THE
AXIS ALONG 22W/23W S OF 18N MOVING W 10 KT. SHOWERS AND TSTMS
HAVE DIMINISHED OVER THE PAST SEVERAL HOURS WITH ONLY ISOLATED
SHOWERS REMAINING WITHIN 50 NM OF THE WAVE AXIS. EVEN THOUGH THE
WAVE LACKS CONVECTION IT STILL SHOWS UP NICELY IN THE UW CIMSS
TPW PRODUCT AND SATELLITE DERIVED WINDS.

A LOW AMPLITUDE TROPICAL WAVE IS ALONG 35W/36W S OF 15N MOVING W
10-15 KT. SATELLITE IMAGERY DEPICTS THIS FEATURE AS A BROAD
LOW-LATITUDE PERTURBATION WITHIN THE ITCZ. DISORGANIZED
SCATTERED SHOWERS ARE WITHIN 150 NM EITHER SIDE OF THE WAVE
AXIS. MORE SIGNIFICANT CONVECTION IS W OF THE WAVE AXIS EMBEDDED
WITHIN THE ITCZ.

A WEAK TROPICAL WAVE IS OVER THE EASTERN CARIBBEAN ALONG 66W.
THE MIMIC TPW ANIMATION SHOWS THE PRESENCE OF THE WAVE WITH A
SURGE OF MOISTURE. MINIMAL SHOWER ACTIVITY IS NOTED.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N17W 10N30W 10N40W 5N55W. NUMEROUS
MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 90 NM EITHER SIDE
OF AXIS BETWEEN 40W-50W. WIDELY SCATTERED MODERATE CONVECTION IS
FROM 5N-11N E OF 19W TO THE COAST OF AFRICA.

DISCUSSION...

GULF OF MEXICO...
ATTENTION REMAINS FOCUSED ON THE DEEP LAYER LOW IN THE ERN GULF
LOCATED NEAR 28N85W. DOPPLER RADAR INDICATES THAT THE ASSOCIATED
DISORGANIZED SHOWER AND TSTM ACTIVITY IS GENERALLY N OF 25N E OF
87W. SEE SPECIAL FEATURE SECTION FOR DETAILS. A SWATH OF VERY
DRY MID TO UPPER AIR CONTINUES TO WRAP AROUND THE PERIPHERY OF
THE UPPER-LEVEL LOW THROUGH THE MIDDLE AND WESTERN GULF THEN E
TO NE ACROSS THE WRN TIP OF CUBA AND THE SE GULF. A NARROW DRY
SLOT CONTINUES NWD ACROSS THE E PART OF THE FL PENINSULA. AN
UPPER TROUGH EXTENDS FROM THE LOW TO THE MEXICAN COAST NEAR
TAMPICO. UPPER RIDGING...CENTERED OVER TEXAS...DOMINATES THE FAR
NW PORTION WHILE A WEAKENING UPPER LOW CONTINUES TO MOVE SLOWLY
OVER CENTRAL MEXICO NEAR 20N100W. DIFFLUENCE ALOFT E OF THIS
UPPER LOW IS PRODUCING ISOLATED SHOWERS IN THE BAY OF CAMPECHE.
ELSEWHERE AT THE SURFACE MODERATE RIDGING DOMINATES THE WESTERN
GULF EXTENDING SWD FROM A 1017 MB HIGH IN ARKANSAS. CONDITIONS
OVER THE NEXT COUPLE OF DAYS HIGHLY DEPEND UPON THE SPECIAL
FEATURE. HOWEVER...REGARDLESS OF DEVELOPMENT...MOISTURE WILL
LIKELY BE ON THE INCREASE ACROSS THE E GULF DRAWN IN BY
EXTENSIVE DEEP SLY FLOW FROM THE TROPICS.

CARIBBEAN SEA...
CLUSTERS OF MODERATE TO ISOLATED STRONG CONVECTION ARE OVER THE
WESTERN CARIBBEAN WEST OF 78W. THIS ACTIVITY IS ASSOCIATED WITH
A SFC TROUGH THAT RUNS FROM 17N83W TO 9N78W AND A DIFFLUENT
PATTERN ALOFT RELATED TO AN UPPER RIDGE THAT COVERS MOST OF THE
WEST AND CENTRAL CARIBBEAN...ANCHORED ON A HIGH OVER NICARAGUA.
THIS RIDGE...COUPLED WITH THE ITCZ IS ALSO ENHANCING CONVECTION
OVER WESTERN VENEZUELA AND NORTHERN COLOMBIA. NW TO WLY UPPER
FLOW...SET UP BETWEEN THE UPPER RIDGE AND AN UPPER-LEVEL LOW
LOCATED JUST N OF HISPANIOLA COVERS THE REGION BETWEEN 64W-74W.
AN UPPER HIGH SITUATED E OF THE LESSER ANTILLES EXTENDS A RIDGE
INTO THE FAR SE PORTION OF THE CARIBBEAN SEA. THE SURFACE PRES
GRADIENT REMAINS FAIRLY RELAXED ACROSS THE AREA...DUE TO THE LOW
IN THE ERN GULF AND WEAK TROUGHING IN THE WRN ATLC. THIS IS
KEEPING THE TRADE WINDS MOSTLY LIGHT...EXCEPT SLIGHTLY STRONGER
NEAR THE COAST OF COLOMBIA. LOOKING AHEAD...LIGHT TO MODERATE
TRADES ARE EXPECTED TO PERSIST TODAY AND SHOWER ACTIVITY WILL
REMAIN FOCUSED IN THE WRN CARIB.

ATLANTIC OCEAN...
SCATTERED SHOWERS AND TSTMS CONTINUE OVER THE WRN ATLC AND THE
NW BAHAMAS W OF 75W ASSOCIATED WITH THE MOIST AND UNSTABLE
ENVIRONMENT E OF THE DEEP LAYER LOW IN THE EASTERN GULF AND
S OF THE STATIONARY COASTAL FRONT JUST OFFSHORE THE CAROLINAS
THROUGH N FLORIDA. UPPER DIFFLUENCE BETWEEN THE UPPER LOW OVER
THE ERN GULF AND AN UPPER HIGH NEAR 29N72W IS ALSO HELPING TO
INDUCE THIS CONVECTIVE ACTIVITY. A WEAK SFC TROUGH ASSOCIATED
WITH THE REMNANTS OF INGRID EXTENDS ALONG 67W/68W FROM 20N-26N.
SCATTERED SHOWERS AND ISOLATED TSTMS ARE RELATED TO THE TROUGH
MAINLY ON THE NORTHERN END. THIS FEATURE IS INTERACTING WITH THE
UPPER LOW LOCATED JUST N OF HISPANIOLA. THE CENTRAL ATLC SFC
PATTERN IS DOMINATED BY A 1011 MB LOW NEAR 33N46W OR ABOUT 870
NM EAST OF BERMUDA. THIS NEARLY STATIONARY NON-TROPICAL LOW IS
BEING MONITORED FOR SIGNS OF TROPICAL DEVELOPMENT. A SFC TROUGH
EXTENDS FROM THE LOW ALONG 24N52W 15N56W. SCATTERED SHOWERS AND
ISOLATED TSTMS ARE FOUND MAINLY EAST AND WITHIN 150 NM OF THE
TROUGH AXIS. THE REMAINDER OF THE E ATLC IS DOMINATED BY TYPICAL
SFC RIDGING S OF A 1027 MB HIGH NE OF THE AZORES NEAR 39N22W.
THIS IS PRODUCING MODERATE NE TRADES E OF 35W...STRONGER NEAR
THE COAST OF NW AFRICA WHERE A TIGHTER PRES GRADIENT EXISTS. A
WEAK SFC TROUGH IS ALONG 28W/29W ASSOCIATED WITH A BENIGN UPPER
LOW NEAR 29N27W WHILE UPPER RIDGING GENERALLY DOMINATES THE
REMAINDER OF THE TROPICAL ATLC.

$$
GR



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