[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 071803
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN OCT 07 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...

A BROAD 1004 MB LOW PRESSURE AREA IS OVER THE NW CARIBBEAN SEA
NEAR 17N82W. THE SYSTEM IS GENERATING SCATTERED SHOWERS AND
TSTMS N OF 12N W OF 78W. THE STRONGEST CLUSTER OF CONVECTION IS
JUST E OF BELIZE WITHIN 60 NM OF 16.5N87W. THE SURROUNDING
BUOY AND SHIP OBSERVATIONS HAVE INDICATED ABOUT A 2-3 MB DROP IN
PRESSURE OVER THE PAST 24 HOURS. HOWEVER...THE OVERALL
CIRCULATION REMAINS RATHER ILL DEFINED AND THE SFC WINDS REMAIN
ON THE LIGHT SIDE. NONETHELESS...UPPER LEVEL WINDS ARE GRADUALLY
BECOMING MORE FAVORABLE AND SLOW DEVELOPMENT OF THIS SYSTEM IS
POSSIBLE OVER THE NEXT FEW DAYS AS IT REMAINS QUASI-STATIONARY.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 54W S OF 20N MOVING W TO NW NEAR 10 KT. A
1009 MB LOW IS LOCATED ALONG THE WAVE AXIS NEAR 17N. THE
CIRCULATION REMAINS AN EXPOSED LOW LEVEL SWIRL...WITH MOST OF
THE LIMITED SHOWER/TSTM ACTIVITY E OF THE CENTER FROM 13N-18N
BETWEEN 49W-54W. DEVELOPMENT OF THIS SYSTEM IS NOT ANTICIPATED
DUE TO UNFAVORABLE UPPER LEVEL WINDS.

...THE ITCZ...
AXIS IS CENTERED ALONG 11N15W 7N30W 10N51W 9N62W. THE ITCZ
REMAINS FAIRLY ACTIVE THIS AFTERNOON. SCATTERED MODERATE
CONVECTION COVERS THE LARGE AREA OVER THE TROPICAL ATLANTIC FROM
3N-11N BETWEEN 21W-50W. THERE MAY BE A WEAK LOW AMPLITUDE WAVE
OR TWO EMBEDDED IN THIS REGION...BUT HAVE HELD OFF ADDING
ANYTHING AT THIS POINT DUE TO THE HIGHLY ZONAL NATURE OF THE
AXIS...WHICH IS MAKING ANY WAVES THAT DO EXIST DIFFICULT TO
TRACK.

DISCUSSION...

THE GULF OF MEXICO...
MODERATE TO FRESH ELY SFC WINDS PERSIST OVER THE E GULF IN
RESPONSE TO A TIGHTENED PRES GRADIENT BETWEEN LOW PRES IN THE NW
CARIBBEAN AND HIGH PRES OVER THE MID-ATLANTIC STATES. THIS STIFF
FLOW IS BLOWING ISOLATED...MOSTLY SHALLOW SHOWERS FROM THE ATLC
ACROSS FLORIDA AND INTO THE E GULF WATERS. THE SFC FLOW REMAINS
LIGHTER W OF 93W AS THE GRADIENT RELAXES. SCATTERED SHOWERS AND
TSTMS ARE A LITTLE MORE CONCENTRATED BETWEEN THE YUCATAN
PENINSULA AND WRN LOUISIANA. THIS ACTIVITY IS ASSOCIATED WITH
DEEP LAYER INVERTED TROUGHING WHICH EXTENDS NWD FROM THE SPECIAL
FEATURE IN THE NW CARIB. SKY CONDITIONS ACROSS MOST OF THE W
GULF W OF 93W ARE MOSTLY CLEAR TO FEW UNDER A MODERATE SUBSIDENT
ENVIRONMENT SUPPORTED BY A CONFLUENT UPPER PATTERN. ELY WINDS
ARE EXPECTED TO REMAIN MODERATE TO FRESH IN THE E AND CENTRAL
GULF OVER THE NEXT DAY OR SO AS THE MOISTURE PLUME AND TROUGHING
FROM THE CARIBBEAN DRIFT W.

THE CARIBBEAN SEA...
THE MAIN AREA OF FOCUS CONTINUES TO BE THE SPECIAL FEATURE
BETWEEN ERN HONDURAS AND THE CAYMAN ISLANDS...WHICH IS BEING
MONITORED FOR SLOW DEVELOPMENT. SEE ABOVE FOR DETAILS.
ELSEWHERE...WIDELY SCATTERED MODERATE CONVECTION IS BETWEEN
69W-78W...BETWEEN SOUTH AMERICA AND HISPANIOLA. THIS IS
SUPPORTED BY CONVERGENT LOW LEVEL FLOW BETWEEN THE S/SW FLOW
AROUND THE SPECIAL FEATURE COLLIDING WITH LIGHT TO MODERATE E-SE
TRADE FLOW OVER THE ERN CARIBBEAN. UPPER FLOW IS ALSO DIFFLUENT
OVER THIS REGION BETWEEN TROUGHING OVER THE NW PORTION AND
RIDGING EXTENDING N ALONG 70W. TRADE FLOW IS EXPECTED TO REMAIN
INTERRUPTED OVER THE NEXT DAY OR SO...WITH THE LOW IN THE NW
PORTION AND TROUGHING PERSISTING IN THE SW NORTH ATLC. THE
EXCEPTION WILL BE MORE OF A NORMAL MODERATE E/ESE BREEZE BETWEEN
THE ABC ISLANDS AND HISPANIOLA.

THE ATLANTIC OCEAN...
MUCH OF THE CENTRAL AND WRN PORTION OF THE DISCUSSION AREA IS
DOMINATED BY AN ELONGATED SFC TROUGH THAT EXTENDS FROM NEAR
28N35W ALL THE WAY BACK TO THE SE BAHAMAS. THE EVOLUTION OF THIS
STRETCHED OUT SFC TROUGHING HAS BEEN THE COMBINED EFFECT OF AN
OLD FRONTAL BOUNDARY...A PAIR OF EX-TROPICAL CYCLONES (KAREN AND
MELISSA)...ENERGY FROM THE TROPICAL WAVE NOW ALONG 54W...AND A
SERIES OF UPPER LOWS AND ASSOCIATED UPPER TROUGHING. NEEDLESS TO
SAY...THE SYSTEM IS VERY COMPLEX. THERE ARE A COUPLE OF AREAS
ALONG THE TROUGHING WHERE LOW LEVEL VORTICITY APPEARS TO BE
MAXIMIZED. IN PARTICULARLY NEAR 26N54W AND 24N69W. NEITHER OF
THESE AREAS ARE GENERATING VERY ORGANIZED TSTM ACTIVITY AT THE
MOMENT THOUGH. HOWEVER...SCATTERED MODERATE CONVECTION IS NORTH
OF PUERTO RICO FROM 20N-25N BETWEEN 65W-69W...AND FURTHER E FROM
24N-26N BETWEEN 58W-64W...AND FINALLY FROM 24N-30N BETWEEN
42W-54W. ELY WINDS REMAINS MODERATE TO FRESH N OF THE TROUGHING
DUE TO THE TIGHTENED GRADIENT BETWEEN THE TROUGH AND HIGH PRES
OVER THE MID ATLC COAST. GFS CONTINUES TO DEVELOP A SERIES OF
LOW PRES AREAS ALONG THE TROUGHING OVER THE NEXT SEVERAL DAYS
THAT MOVE NE/ENE ALONG THE BOUNDARY...BUT CURRENTLY HAVE LOW
CONFIDENCE IN THESE LOWS WITH FAIRLY WIDE DIVERGENCE BETWEEN THE
GLOBAL MODELS.

MUCH QUIETER WEATHER EXISTS E OF 35W. THE MAIN MID TO UPPER
LEVEL FEATURE OVER THE TROPICS IS AN ANTICYCLONE CENTERED
NEAR 11N37W.  IN THE SUBTROPICS...THE UPPER FLOW IS QUITE STRONG
OUT OF THE W TO SW ON THE N SIDE OF THE TROPICAL RIDGE. THIS
SWIFT FLOW IS SPREADING DEBRIS MOISTURE ACROSS MUCH OF THE AREA
N OF 23N W OF THE CANARY ISLANDS...EXCEPT FOR MUCH DRIER AIR N
OF 25N BETWEEN 20W-30W...BEHIND AN UPPER TROUGH. THE SFC PATTERN
IS RATHER TRANQUIL WITH A 1022 MB HIGH CENTERED NEAR
29N28W. THIS IS KEEPING WINDS LIGHT IN THE SUBTROPICS AND
MODERATE IN THE TROPICS...EXCEPT SLIGHTLY STRONGER 20-25 KT NLY
WINDS OFF THE COAST OF NW AFRICA WHERE THE GRADIENT REMAINS
TIGHTER PER USUAL.

$$
WILLIS


WWWW
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