[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 231744
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN SEP 23 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURE...
JERRY HAS BEEN BORN FAR FROM ANY LAND AREAS. AT 23/1500 UTC THE
CENTER OF SUBTROPICAL STORM JERRY IS CENTERED NEAR 36.0N 46.3W
OR ABOUT 930 NM W OF THE AZORES AND IS NEARLY STATIONARY.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1004 MB. MAXIMUM SUSTAINED
WIND SPEED IS 35 KT WITH GUSTS TO 45 KT. SEE LATEST NHC FORECAST
ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 FOR MORE
DETAILS. THE SUBTROPICAL STORM IS A VERY BROAD CYCLONE WITH
SEVERAL SWIRLS NEAR THE ESTIMATED CENTER. ASSOCIATED CONVECTION
IS ALSO BROAD AND NOT VERY WELL ORGANIZED WITH IR IMAGERY
SUGGESTING SCATTERED MODERATE WITHIN 240 NM SW AND 180 NM NE
QUADRANTS. A LARGER AREA OF CONVECTION IS LOCATED TO THE S OF
THE SYSTEM IN AN UPPER DIFFLUENT ZONE. THERE IS A NARROW WINDOW
FOR JERRY TO ACQUIRE TROPICAL CHARACTERISTICS BEFORE BEING
ABSORBED BY A LARGE EXTRATROPICAL LOW.

A BROAD LOW PRES TROUGH EXTENDS FROM THE YUCATAN PENINSULA NWD
INTO THE CENTRAL GULF OF MEXICO. THIS SFC LOW PRES AREA...ALONG
WITH EXTENSIVE SLY UPPER FLOW...IS GENERATING A LARGE AREA OF
SCATTERED SHOWERS AND TSTMS FROM THE W CARIB NWD THROUGH THE
CENTRAL GULF BETWEEN 86W-91W. THIS SYSTEM HAS NOT BECOME ANY
BETTER ORGANIZED SO FAR TODAY. HOWEVER THERE IS A POTENTIAL FOR
DEVELOPMENT IN THE AREA.

A WELL DEFINED TROPICAL WAVE IS LOCATED ALONG 54W/55W OR ABOUT
300 NM E OF THE WINDWARD ISLANDS. THIS WAVE IS FAIRLY ACTIVE
GENERATING CLUSTERS OF SCATTERED MODERATE CONVECTION WITHIN 180
NM OF THE AXIS. THIS SYSTEM IS SHOWING SIGNS OF ORGANIZING AND
IT COULD DEVELOP INTO A TROPICAL DEPRESSION OVER THE NEXT DAY OR
SO AS IT APPROACHES THE WINDWARD ISLANDS. REGARDLESS OF
DEVELOPMENT...ASSOCIATED SHOWERS AND TSTMS WILL BEGIN TO SPREAD
ACROSS THOSE ISLANDS LATER TONIGHT AND TOMORROW.

A FAIRLY LARGE ACTIVE LOW PRES SYSTEM IS LOCATED ABOUT 550-600
NM SW OF THE CAPE VERDE ISLANDS NEAR 6.5N28W...ESTIMATED TO BE
1007 MB. THERE IS A FAIR AMOUNT OF CONVECTION ESPECIALLY TO THE
N OF THE CENTER. LATEST IR IMAGES SHOW THE CONVECTION WEAKENING
SLIGHTLY...STILL SCATTERED MODERATE IS WITHIN 400 NM N AND 90 NM
S SEMICIRCLES. OVERALL...THE SYSTEM IS GRADUALLY BECOMING BETTER
ORGANIZED AND CONDITIONS ARE FAVORABLE FOR IT TO BECOME A
TROPICAL DEPRESSION DURING THE NEXT DAY OR TWO.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 35W S OF 18N MOVING W 10-15 KT. THIS WAVE
HAS MAINTAINED GOOD WWD CONTINUITY IN BOTH SATELLITE HOVMOLLER
DIAGRAMS AND THE MIMIC TPW ANIMATION SINCE EMERGING OFF THE
COAST OF AFRICA A FEW DAYS AGO. HOWEVER...THE LARGE AND ACTIVE
LOW PRES SYSTEM E OF THE WAVE...ERN MOST SPECIAL FEATURE
DISCUSSED ABOVE...IS BEGINNING TO OVERTAKE THIS WAVE AS
INDICATED BY A RECENT QSCAT PASS WHICH SHOWS IT EMBEDDED WITHIN
THE CIRCULATION OF THE LARGER LOW. IN ADDITION...THE ONCE
AMPLIFIED MOISTURE SURGE ON THE MIMIC ANIMATION HAS LOST
LATITUDE AND BECOME WEAKER ALSO SUGGESTING AN ABSORPTION PROCESS
UNDERWAY.

TROPICAL WAVE IS IN THE W CARIBBEAN ALONG 82W S OF 19N MOVING W
10-15 KT. THE WAVE IS NOT EASILY SEEN IN ANY OF THE AVAILABLE
DATA...THEREFORE THE WAVE POSITION IS BASED ON FORWARD
EXTRAPOLATION. THIS WEAK SYSTEM LIES UNDERNEATH AN UPPER
DIFFLUENT ZONE WHICH IS FUELING SCATTERED MODERATE CONVECTION IN
THE REGION. REFER TO THE CARIBBEAN SECTION BELOW FOR DETAILS.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 5N9W 10N23W 7N34W 5N35W 11N51W. IT
SHOULD BE NOTED THAT THE AXIS APPEARS DISCONTINUOUS IN THE FAR E
ATLC AND OVER AFRICA WITH THAT AXIS STRETCHING TO 13N17W. THERE
IS NO SIGNIFICANT CONVECTION BESIDES FOR THE ACTIVITY ASSOCIATED
WITH THE SPECIAL FEATURES.

DISCUSSION...

GULF OF MEXICO...
IR IMAGERY AND LIGHTNING DATA REVEAL A LARGE AREA OF CLOUDINESS
...SCATTERED SHOWERS AND TSTMS EXTENDING FROM THE W CARIB NWD
THROUGH THE CENTRAL GULF BETWEEN 86W-91W. AN ILL-DEFINED LOW
PRES TROUGH LIES ACROSS THE AREA...WITH VISIBLE IMAGERY
SUGGESTING A BROAD LOW JUST N OF THE NRN YUCATAN PENINSULA.
REFER TO THE SPECIAL FEATURE SECTION ABOVE FOR DETAILS.
STRONG SLY UPPER FLOW...BETWEEN AN UPPER HIGH CENTERED NEAR
23N84W AND AN UPPER LOW NEAR BROWNSVILLE TEXAS...IS LIKELY
ENHANCING AND ADVECTING THE MOISTURE PLUME DESCRIBED ABOVE. SOME
OF THE MOISTURE IS NOW SPREADING INLAND OVER THE WRN FLORIDA
PANHANDLE AND GULF COAST PORTIONS OF ALABAMA AND MISSISSIPPI.
DOPPLER RADAR SHOWS QUICK MOVING STREAMS OF SHOWERS SPREADING
ACROSS S AND CENTRAL FLORIDA FROM THE ATLC. THESE SHOWERS ARE
BEING STEERED BY THE LOW-LEVEL FLOW. DRY STABLE AIR LIES ACROSS
THE REGION W OF 93W ALLOWING SKIES TO BE FAIR TO MOSTLY CLEAR.

CARIBBEAN SEA...
CLUSTERS OF SCATTERED MODERATE CONVECTION ARE PERSISTING ACROSS
THE W CARIB AND PORTIONS OF ERN NICARAGUA AND HONDURAS...
GENERALLY W OF 82W. THIS ACTIVITY IS BEING ENHANCED BY A TROUGH
OF LOW PRES OVER THE YUCATAN PENINSULA AND DIFFLUENCE ALOFT. AN
UPPER LOW IS LOCATED ABOVE THE S CENTRAL CARIB NEAR 13N75W. NLY
FLOW TO THE W OF THE LOW IS DRAWING IN DRIER AIR BETWEEN IT AND
ABOUT 80W. A LINGERING WEAK SFC TROUGH IS LOCATED OVER THE E
CARIB WITH THE AXIS EXTENDING FROM 14N62W NNE ACROSS THE LESSER
ANTILLES. LIGHT WINDS AROUND THE TROUGH IS PROVIDING LIMITED
LOW-LEVEL CONVERGENCE GENERATING ONLY SCATTERED CLOUDINESS AND
ISOLATED SHOWERS WITHIN 60 NM OF THE AXIS. THE REMAINDER OF THE
REGION IS EXPERIENCING TRANQUIL CONDITIONS. HOWEVER...AN
INCREASE IN MOISTURE IS NOT FAR OFF AS A STRONG TROPICAL WAVE
MOVES INTO THE E CARIB OVER THE NEXT DAY OR SO.

ATLANTIC OCEAN...
MOST OF THE ACTIVE SFC FEATURES ARE DISCUSSED IN THE SPECIAL
FEATURES SECTION ABOVE. ELSEWHERE AT THE SFC...WEAK HIGH PRES
RIDGING CONTROLS THE W ATLC WITH A 1020 MB HIGH CENTERED NEAR
35N59W. A DISSIPATING COLD FRONT INTERRUPTS THIS RIDGING ONLY
SLIGHTLY RUNNING FROM 32N68W TO 29N77W. TROUGHING DOMINATES THE
CENTRAL ATLC ZONE TO THE S OF NEWLY UPGRADED SUBTROPICAL STORM
JERRY AND ENHANCED BY A LINGERING LOW-LEVEL TROUGH WHICH EXTENDS
NWD FROM THE E CARIB ALONG 18N61W 25N56W. MODERATE RIDGING TAKES
OVER IN THE E ATLC ANCHORED BY A 1026 MB CENTERED TO THE E OF
THE AZORES NEAR 39N21W. THIS OVERALL PATTERN IS PRODUCING
MODERATE TRADES IN THE E ATLC...EXCEPT STRONG NEAR THE TYPICAL
TIGHTENED GRADIENT NEAR THE COAST OF NW AFRICA. LIGHT TO
MODERATE WINDS EXIST ELSEWHERE IN THE FAIRLY RELAXED GRADIENT.

IN THE MID AND UPPER LEVELS...NLY FLOW AROUND THE E PERIPHERY OF
THE SE GULF HIGH IS ADVECTING MID-HIGH CLOUDINESS AND ISOLATED
SHOWERS W OF 70W. A WEAK SHORTWAVE APPEARS EMBEDDED IN THAT FLOW
DEEPENING THE MOISTURE A BIT. THE FLOW THEN FOLDS INTO A VERY
BROAD TROUGH COVERING THE AREA BETWEEN 45W-70W. THIS TROUGH IS
PROVIDING SOME SUPPORT FOR THE WEAK LOW-LEVEL BOUNDARY IN THE
CENTRAL ATLC DISCUSSED ABOVE. THE COMBINATION OF THE TWO IS
PRODUCING SCATTERED SHOWERS AND ISOLATED TSTMS WITHIN 120 NM E
OF THE TROUGH AXIS AND N OF 25N BETWEEN 40W-51W. AN AMPLIFIED
UPPER RIDGE TAKES OVER E OF THE TROUGH WITH THE AXIS EXTENDING
ROUGHLY N-S ALONG 35W/36W. A LARGE UPPER LOW IS SITUATED E OF
THE RIDGE W OF THE MADEIRA ISLANDS NEAR 33N21W. THIS LOW IS
PROVIDING PRONOUNCED TROUGHING ACROSS THE NEARLY THE ENTIRE ATLC
E OF 30W. SWLY FLOW ON THE E SIDE OF THE LOW IS GENERATING
SCATTERED CLOUDINESS AND ISOLATED SHOWERS OVER AND TO THE W OF
THE CANARY ISLANDS.

$$
CANGIALOSI


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