[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 131728
TWDAT

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

...TROPICAL WAVES...

TROPICAL WAVE IS ADDED TO THE 12Z ANALYSIS JUST E OF THE CAPE
VERDE ISLANDS ALONG 22W/23W S OF 17N ESTIMATED TO BE MOVING W
10-15 KT. SURFACE OBSERVATIONS AND SOUNDING DATA FROM DAKAR
SUGGEST A FAIRLY SHALLOW WAVE PASSAGE SOMETIME AROUND 18Z
YESTERDAY. ITS TOUGH TO SEE GOOD CONTINUITY IN SATELLITE
HOVMOLLER DIAGRAMS DUE TO AN ABUNDANT AMOUNT OF HIGH LEVEL
CLOUDINESS ASSOCIATED WITH AN UPPER JET.  HOWEVER...THIS WAVE IS
FAIRLY EASY TO LOCATE ON TODAY'S VISIBLE IMAGERY AS A FAIRLY
CLASSIC LOW AMPLITUDE INVERTED V-SHAPE IS EVIDENT. SCATTERED
SHOWERS AND ISOLATED TSTMS ARE WITHIN 180 NM EITHER SIDE OF THE
AXIS.

TROPICAL WAVE IS ALSO ADDED ALONG 42W S OF 14N ESTIMATED TO BE
MOVING W 10-15 KT. THERE HAS BEEN SOME EVIDENCE OF THIS WAVE
OVER THE PAST FEW DAYS...AS SEEN IN THE MIMIC TPW ANIMATION AND
SATELLITE HOVMOLLER DIAGRAMS...THOUGH IS HAS BEEN VERY
LOW-LATITUDE AND EMBEDDED WITHIN THE ITCZ. HOWEVER...THE WAVE
HAS GAINED CONVECTION TODAY AS IT CURRENTLY LIES NEAR THE RIGHT
ENTRANCE REGION OF A SWLY JET BRANCH. SCATTERED SHOWERS AND
TSTMS ARE SHEARED TO THE E OF THE AXIS WITHIN 240 NM FROM
9N-12N.

TROPICAL WAVE IS IN THE CENTRAL CARIBBEAN ALONG 73W S OF 18N
MOVING W 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. MORE OF THE SAME TODAY...SCATTERED
SHOWERS AND TSTMS ARE CURRENTLY WITHIN 240 NM EITHER SIDE OF THE
WAVE AXIS.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N16W 10N25W 8N41W 10N63W. BESIDES
FOR THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES ...
SCATTERED MODERATE IS FROM 6N-10N BETWEEN 15W-19W AND FROM
10N-12N BETWEEN 28W-30W. ISOLATED MODERATE IS WITHIN 180 NM N OF
THE AXIS W OF 44W.

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 85W AND CONFLUENCE ALOFT TO THE NW OF A JET BRANCH OVER
THE BAHAMAS. THIS SINKING AIR IS SUPPRESSING DEEP CLOUD
FORMATION AND PROVIDING A NICE WEATHER DAY ACROSS THE REGION. A
VERY SLIGHT INTERRUPTION IS IN THE SW GULF NEAR A SFC TROUGH
WHICH EXTENDS FROM THE YUCATAN PENINSULA TOWARD BROWNSVILLE
TEXAS ALONG 20N90W 27N96W. ONLY 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. HOWEVER...MODEL
GUIDANCE SHOWS THE GRADIENT TIGHTENING OVER THE NEXT DAY OR TWO
SO WINDS ARE FORECAST TO INCREASE.

CARIBBEAN SEA...
A BROAD AREA OF LOW PRES HAS DRIFTED TO THE E SLIGHTLY CENTERED
OFF THE COAST OF BELIZE NEAR 18N86W...ANALYZED 1007 MB AT 15Z.
THIS LOW EXTENDS AN ELONGATED TROUGH NEWARD ACROSS WRN CUBA AND
SWD INTO HONDURAS AND GUATEMALA. DISORGANIZED SCATTERED SHOWERS
AND TSTMS ARE WITHIN 120 NM W OF THE TROUGH AXIS S OF 20N.
SIMILAR ACTIVITY IS LOCATED FURTHER TO THE NE OVER CENTRAL CUBA
AND THE BAHAMAS N OF 20N BETWEEN 77W-79W...LIKELY ENHANCED BY
THE UPPER JET MENTIONED IN THE GULF SECTION. ANY FURTHER
DEVELOPMENT OF THIS SYSTEM IS EXPECTED TO BE SLOW TO OCCUR
BEFORE IT DRIFTS BACK WWD OVER LAND ON SUNDAY. HEAVY RAINS ARE
POSSIBLE 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 S 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 JUST N OF HAITI
AND A BROAD UPPER LOW JUST E OF TRINIDAD. 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 NW 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 LOTS OF CLOUDINESS ROUGHLY BETWEEN 60W-80W. SCATTERED
SHOWERS AND TSTMS ARE MAINLY CONFINED N OF 25N BETWEEN 60W-68W
AND S OF 25N BETWEEN 74W-79W. 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 40N33W.
THE PERSISTENT LOW NEAR THE CANARY ISLANDS HAS OPENED INTO A
TROUGH EXTENDING FROM 31N13W 26N16W...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. A QSCAT PASS AROUND 0930Z SHOWED 20-25 KT IN
THE ERN SEMICIRCLE. THIS SAME DATA REVEALS LIGHT WINDS ACROSS
THE SUBTROPICS AND MODERATE 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 20N16W. THIS JET IS SHEARING THE TROPICAL
WAVES ALONG 22W AND 42W AND SPREADING HIGH LEVEL CLOUDINESS
ACROSS THE TROPICAL E ATLC.

$$
CANGIALOSI




This weather bulletin was brought to you by:
www.nashvilleweather.net