[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 132342
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SAT OCT 13 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS NEAR THE EASTERN CAPE VERDE ISLANDS ALONG 23W S
OF 17N ESTIMATED TO BE MOVING W NEAR 15 KT. SURFACE OBSERVATIONS
AND SOUNDING DATA FROM DAKAR SUGGEST A FAIRLY SHALLOW WAVE
PASSAGE SOMETIME AROUND 18Z YESTERDAY.  THIS WAVE IS FAIRLY EASY
TO LOCATE IN SATELLITE IMAGERY WITH A CLASSIC LOW AMPLITUDE
INVERTED V-SHAPE EVIDENT. DISORGANIZED SCATTERED SHOWERS AND
ISOLATED TSTMS ARE WITHIN 180 NM EITHER SIDE OF THE AXIS. THE
CLOUD TOPS OVER THIS ACTIVITY ARE BEING SHEARED TO THE NE BY SW
FLOW ALOFT...MAINLY N OF 9N.

A LOW AMPLITUDE TROPICAL WAVE IS ALONG 43W S OF 14N ESTIMATED TO
BE MOVING W 10-15 KT. LOW TO MID LEVEL CYCLONIC TURNING REMAINS
EVIDENT AROUND THE AXIS IN THIS EVENINGS SHORTWAVE IR IMAGERY.
SCATTERED MODERATE CONVECTION IS MOSTLY DISPLACED WITHIN 180NM E
OF THE AXIS DUE TO W-SW FLOW ALOFT.

TROPICAL WAVE IS IN THE CENTRAL CARIBBEAN ALONG 74W S OF 18N
MOVING W NEAR 10 KT OVER THE PAST 24 HOURS. THIS WAVE HAS
CARRIED A FAIR AMOUNT OF CLOUDINESS AND DISORGANIZED SHOWER
ACTIVITY OVER THE PAST COUPLE OF DAYS. SCATTERED SHOWERS AND
ISOLATED TSTMS ARE CURRENTLY WITHIN 210 NM EITHER SIDE OF THE
WAVE AXIS...AFFECTING COASTAL COLOMBIA N THROUGH HISPANIOLA.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N15W 7N30W 9N41W 9N63W. BESIDES
FOR THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES
...SCATTERED MODERATE TO STRONG CONVECTION IS ALONG THE COAST OF
W AFRICA FROM 7N-13N BETWEEN 11W-16W. SCATTERED MODERATE IS ALSO
FROM 5N-12N BETWEEN 28W-33W...WHICH MAY BE ASSOCIATED WITH
ANOTHER LOW AMPLITUDE TROPICAL WAVE.

DISCUSSION...

GULF OF MEXICO...
ABUNDANT DRY STABLE AIR IN THE MID AND UPPER LEVELS DOMINATES
THE GULF. THIS STABLE AIRMASS IS ENHANCED BY AN UPPER SHORTWAVE
ALONG 84W AND CONFLUENCE ALOFT TO THE NW OF A JET BRANCH OVER
THE BAHAMAS. THIS SINKING AIR IS SUPPRESSING DEEP CLOUD
FORMATION AND PROVIDING NICE WEATHER ACROSS THE REGION. THE ONLY
EXCEPTION IS IN THE SW GULF NEAR A SFC TROUGH WHICH EXTENDS FROM
THE YUCATAN PENINSULA TOWARD BROWNSVILLE TEXAS ALONG 18N92W
26N97W. ISOLATED SHALLOW SHOWERS ARE POSSIBLE WITHIN 60 NM OF
THIS LINE. THE LARGER SCALE SFC PICTURE CONSISTS OF HIGH PRES TO
THE N OF THE AREA OVER THE OHIO VALLEY AND LOW PRES TO THE S IN
THE NW CARIB. THIS PATTERN IS PRODUCING NELY WINDS MAINLY IN THE
10-15 KT RANGE. MODEL GUIDANCE SHOWS THE GRADIENT TIGHTENING
SLIGHTLY OVER THE NEXT DAY OR TWO SO WINDS ARE FORECAST TO
INCREASE A TOUCH...AND VEER AS THE HIGH N OF THE AREA MOVES E.

CARIBBEAN SEA...
A BROAD AREA OF LOW PRES IS OVER THE GULF OF HONDURAS...ANALYZED
1005 MB AT 2100 UTC NEAR 17N86W OR JUST N OF THE ISLAND OF
ROATAN. AN ELONGATED TROUGH EXTENDS NEWARD FROM THE LOW ACROSS
WRN CUBA. DISORGANIZED CLOUDINESS...SHOWERS AND TSTMS ASSOCIATED
WITH THIS SYSTEM ARE OVER PORTIONS OF THE NW CARIBBEAN. A
STRONGER CLUSTER OF CONVECTION IS NOTED BETWEEN THE CAYMAN
ISLANDS AND ERN CUBA...N OF 19N BETWEEN 76W-81W. THIS ACTIVITY
IS LIKELY BEING ENHANCED BY THE UPPER JET MENTIONED IN THE GULF
SECTION.  ALTHOUGH NUMERICAL GUIDANCE DOES NOT SHOW TROPICAL
CYCLONE FORMATION IN THIS AREA...ENVIRONMENTAL CONDITIONS APPEAR
TO BE FAVORABLE FOR SOME SLOW DEVELOPMENT BEFORE THE SYSTEM
MOVES OVER YUCATAN IN A DAY OR SO. REGARDLESS OF
DEVELOPMENT...HEAVY RAINS ARE EXPECTED TO CONTINUE OVER CENTRAL
AMERICA FOR THE NEXT FEW DAYS...ESPECIALLY OVER PORTIONS OF THE
PACIFIC COAST.

ANOTHER MASS OF CLOUDINESS AND DISORGANIZED SHOWERS AND TSTMS
ARE AFFECTING A PORTION OF THE CENTRAL CARIBBEAN ASSOCIATED WITH
A TROPICAL WAVE. FOR DETAILS REFER TO THAT SECTION ABOVE. THE
ERN CARIB IS RATHER TRANQUIL LYING IN AN UPPER CONFLUENT ZONE
BETWEEN A WELL DEFINED UPPER HIGH CENTERED NEAR THE WINDWARD
PASSAGE AND A BROAD UPPER LOW NEAR THE WINDWARD ISLANDS. ELY
TRADES ARE MODERATE E OF THE TROPICAL WAVE BUT REMAIN
INTERRUPTED IN THE W CARIB DUE TO THE PRESENCE OF THE BROAD LOW
PRES TROUGH.

ATLANTIC OCEAN...
A SLOW MOVING FRONTAL BOUNDARY WITH A SERIES OF WEAK LOWS JUST N
OF THE AREA ENTERS THE REGION NEAR 32N62W AND EXTENDS SW TOWARD
THE CENTRAL BAHAMAS. THE SRN PORTION OF THE BOUNDARY LACKS UPPER
SUPPORT AT THE MOMENT WITH EXTENSIVE STRONG SWLY FLOW ABOVE IT.
HOWEVER...SOME SUPPORT IS NOT FAR AWAY WITH A SHORTWAVE NEARING
FLORIDA. GFS RESPONDS TO THIS DEVELOPING A COUPLE OF LOWS ALONG
THE BOUNDARY NEAR AND NE OF THE BAHAMAS OVER THE NEXT DAY OR
TWO. THE COMBINATION OF LOW-LEVEL CONVERGENCE AND A PLENTIFUL
AMOUNT OF UPPER MOISTURE...ADVECTED BY THE STRONG SWLY FLOW...IS
PRODUCING ABUNDANT CLOUDINESS ROUGHLY BETWEEN 60W-80W. SCATTERED
SHOWERS AND TSTMS ARE MAINLY CONFINED TO THE REGION WITHIN 180NM
E OF THE FRONT. THE TIGHTENED PRES GRADIENT BETWEEN THE
FRONT...LOW PRES IN THE CARIB AND HIGH PRES OVER THE OHIO VALLEY
IS PRODUCING MODERATE NE-E WINDS ACROSS THE NW BAHAMAS AND S
FLA.

CONDITIONS ARE FAIRLY TRANQUIL ACROSS MUCH OF THE CENTRAL AND E
ATLC. THE SFC PATTERN IS CONTROLLED BY RIDGING EXTENDING SWD
FROM A 1027 MB HIGH SITUATED JUST W OF THE AZORES NEAR 39N34W.
SFC TROUGHING CONTINUES TO EXTEND SW THROUGH THE CANARY
ISLANDS...BUT BESIDES FOR THE WIND SHIFT CLEARLY NOTED OVER
THOSE ISLANDS THERE IS LITTLE OTHER EFFECTS. THE REMNANTS OF
T.D. 15 IS STILL SPINNING ALONG OUR N BORDER NEAR 32N50W...AND
IS NOT GENERATING MUCH SIGNIFICANT WEATHER AT THE MOMENT. EXCEPT
FOR A SMALL AREA OF MODERATE SW WINDS JUST AHEAD OF THE NRN
PORTION OF THE W/CENTRAL ATLC FRONT...WINDS ARE LIGHT OVER THE
REMAINDER OF THE SUBTROPICAL PORTION OF THE DISCUSSION
AREA...WHILE MODERATE TRADES PERSIST IN THE TROPICS. THE UPPER
PATTERN CONSISTS OF AN ELONGATED RIDGE/TROUGH PATTERN. A SWLY
JET BRANCH ORIGINATES JUST TO THE E OF THE BASE OF THE TROUGH
AND EXTENDS NE TO AFRICA NEAR 20N17W. THIS JET IS SHEARING THE
TROPICAL WAVES ALONG 23W AND 43W AND SPREADING HIGH LEVEL
CLOUDINESS ACROSS THE TROPICAL E ATLC.

$$
WILLIS/CANGIALOSI




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