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Tropical Discussion
 
(Latest Discussion - Issued 1749Z Oct 27, 2021)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
149 PM EDT WED OCT 27 2021

TROPICAL DISCUSSION FROM OCT 27/18 UTC: AT MID/UPPER LEVELS...A
BROAD/LOW AMPLITUDE POLAR TROUGH IS INITIALIZED OVER THE WESTERN
ATLANTIC...WITH AXIS BOTTOMING OUT NORTH OF THE ISLANDS. THROUGH
THE DAY TODAY THE BASE OF THE MID LEVEL TROUGH IS FORECAST TO PULL
WHILE LIFTING OVER A RIDGE TO THE EAST. AT LOW LEVELS...THE TROUGH
SUSTAINS A SURFACE FRONT OVER THE WESTERN ATLANTIC...THAT IS TO
TRAIL ACROSS THE CENTRAL BAHAMAS-FLORIDA KEYS TO THE EASTERN GULF
LATER THIS AFTERNOON. ON THURSDAY...AS IT LOSES UPPER LEVEL
SUPPORT...THE FRONT IS TO THEN RETROGRESS. MEANWHILE...ACROSS THE
CENTRAL AND SOUTHEAST BAHAMAS EXPECTING RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15MM IN FRONTAL CONVECTION...WHILE
ACROSS CUBA EXPECTING SIMILAR AMOUNTS IN PREFRONTAL CONVECTION.

CONSISTENT WITH PREVIOUS FORECASTS...A DEEPER/HIGHER AMPLITUDE
TROUGH CLOSELY FOLLOWS...WITH THE MID/UPPER LEVEL TROUGH TO
AMPLIFY ACROSS THE CENTRAL USA TO THE NORTHWEST GULF OF MEXICO
EARLY ON THURSDAY MORNING. THE DEEP TROUGH WILL THEN BECOME THE
DOMINANT SYNOPTIC SCALE FEATURE ACROSS THE CENTRAL/EASTERN USA AND
THE GULF OF MEXICO ON THURSDAY TO FRIDAY. IT IS TO THEN MEANDER
EAST ACROSS THE EASTERN USA TO THE WESTERN ATLANTIC DURING THE
WEEKEND. AT LOW LEVELS...DRIVEN BY A NORTHERLY LOW LEVEL JET...THE
ASSOCIATED FRONT SURGES ACROSS THE NORTHWEST GULF TO VERACRUZ
MEXICO LATER TODAY. ON THURSDAY THE FRONT CONTINUES ACROSS FLORIDA
TO THE NORTHWEST BAHAMAS WHILE TRAILING ACROSS WESTERN CUBA/THE
YUCATAN TO THE SOUTHERN STATES OF MEXICO. THROUGH FRIDAY THE FRONT
SINKS FARTHER SOUTH ACROSS CENTRAL CUBA TO THE NORTHWEST CARIBBEAN
WHILE TRAILING ACROSS GUATEMALA TO SOUTHERN MEXICO. OVER
VERACRUZ...PREFRONTAL CONVECTION WILL RESULT IN RAINFALL AMOUNTS
OF 05-10MM/DAY AND ISOLATED MAXIMA OF 15MM LATER TODAY. ON
THURSDAY THIS WILL INCREASE TO 15-20MM/DAY AND MAXIMA OF 30-60MM
WHILE BUILDING ACROSS VERACRUZ TO TABASCO/CAMPECHE AND CHIAPAS IN
SOUTHERN MEXICO TO NORTHERN GUATEMALA...WHILE ACROSS THE NORTHWEST
BAHAMAS TO WESTERN CUBA AND THE YUCATAN IT WILL SUSTAIN RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM. ON FRIDAY ACTIVITY
ACROSS THE NORTHWEST BAHAMAS INTENSIFIES WITH RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-35MM...WHILE OVER CUBA EXPECTING
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-25MM. OVER BELIZE AND
GUATEMALA THIS WILL THEN TRIGGER ADDITIONAL RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-35MM. HIGHER AMOUNTS ARE EXPECTED
OVER NORTHWEST HONDURAS ON FRIDAY TO SATURDAY...WITH RAINFALL
AMOUNTS 20-40MM/DAY AND MAXIMA OF 75-125MM.

AS THE AFOREMENTIONED TROUGH DEEPENS OVER THE USA/GULF OF
MEXICO...IN A SINUSOIDAL PATTERN...CELL OF THE SUBTROPICAL RIDGE
OVER THE EASTERN CARIBBEAN WILL SIMULTANEOUSLY BUILD NORTH ACROSS
THE NORTHEAST CARIBBEAN ISLANDS TO THE WESTERN ATLANTIC. BROAD MID
LEVEL RIDGE IS TO THEN SETTLE OVER THE WESTERN ATLANTIC LATER IN
THE WEEK. AS THE RIDGE BUILDS NORTH OF THE ISLANDS A TUTT WILL
THEN AMPLIFY ACROSS THE NORTHEAST CARIBBEAN LATER ON FRIDAY/EARLY
ON SATURDAY. THROUGH THE WEEKEND THIS WILL THEN EVOLVE INTO A
CLOSED MID/UPPER LEVEL LOW OVER THE NORTHEAST CARIBBEAN.
INITIALLY...UNDER THE INFLUENCE OF THE MID LEVEL RIDGE...A FAIRLY
STRONG TRADE WINDS INVERSION IS TO ENVELOP THE NORTHEAST CARIBBEAN
ISLANDS. ACROSS HISPANIOLA-PUERTO RICO AND THE LEEWARD ISLANDS
THIS WILL THEN FAVOR FAIR WEATHER CONDITIONS. BUT AS THE TUTT
DEEPENS DURING THE WEEKEND...THE COLD CORE MID/UPPER LEVEL LOW
WILL ENHANCE CONVECTIVE INSTABILITY ACROSS THE NORTHEAST
CARIBBEAN. BEST FORCING WITH THIS FEATURE...HOWEVER...IS EXPECTED
TO THE SOUTH AS IT INTERACTS WITH THE ITCZ/NEAR EQUATORIAL TROUGH
OVER NORTHEAST VENEZUELA/NORTHERN GUIANA AND TRINIDAD/THE SOUTHERN
WINDWARD ISLANDS.

TROPICAL WAVES/TUTT INDUCED PERTURBATIONS/TRADE WIND SURGES
INITIALIZED AT 12 UTC:
TYPE  INIT  SOF 28/00 28/12 29/00 29/12 30/00 30/12 31/00
TW     43W  09N   45W   48W   51W   54W   57W   59W   61W
TI/EW  54W  25N   56W   58W   60W   61W   63W   66W   68W
TW     76W  15N   78W   80W   81W/LOW SRN CARIBBEAN

A TROPICAL WAVE IS INITIALIZED ALONG 43W AND SOUTH OF 09N. MOVES
NORTH OF FRENCH GUIANA ON FRIDAY...WITH MOST ACTIVE CONVECTION
EXPECTED TO THE NORTH ALONG THE ITCZ. ON FRIDAY IT PHASES WITH A
PERTURBATION TO THE SOUTH AS IT ENTERS GUYANA..TO SUSTAIN RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM...WITH SIMILAR AMOUNTS
ACROSS TRINIDAD AND NORTHEAST VENEZUELA.

A TUTT INDUCED PERTURBATION/EASTERLY WAVE ALONG 54W AND SOUTH OF
25N IS NOW EXPECTED TO PERSIST AS IT INTERACTS WITH TUTT LOW
DEEPENING ACROSS THE NORTHEAST CARIBBEAN. ACROSS THE
FRENCH...LEEWARD/VIRGIN ISLES AND PUERTO RICO IT IS TO SUSTAIN
LIGHT CONVECTION WITH RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA
OF 10MM ON SATURDAY.

A TROPICAL WAVE ALONG 76W AND SOUTH OF 15N IS FORECAST TO ORGANIZE
INTO A CLOSED LOW OVER THE SOUTHERN CARIBBEAN/NORTH OF PANAMA
EARLY ON FRIDAY MORNING. THIS IS DRAWING THE NET NORTH ACROSS
NORTHERN COLOMBIA/VENEZUELA-ABC ISLANDS EARLY IN THE CYCLE...WHERE
IT IS TO REMAIN THROUGH THE END OF THE WEEK. THE AFOREMENTIONED
TUTT...AS IT AMPLIFIES ACROSS THE EASTERN CARIBBEAN...IT IS TO
INTERACT WITH THIS FEATURE. OVER THE ABC ISLANDS-NORTHERN
COLOMBIA/NORTHWEST VENEZUELA THIS WILL FAVOR RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15-20MM THROUGH THE DAY TODAY...WHILE
ACROSS TRINIDAD/ORINOCO DELTA EXPECTING RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-30MM. ACTIVITY ACROSS NORTHERN
COLOMBIA/NORTHWEST VENEZUELA IS TO ALSO INTENSIFY...WITH MAXIMA OF
10-15MM/DAY AND MAXIMA OF 20-45MM ON THURSDAY TO FRIDAY...WHILE ON
FRIDAY TO SATURDAY THE MAXIMA DROPS TO 20-35MM. OVER PANAMA AND
COSTA RICA INITIALLY EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-25MM. BUT AS THE LOW FORMS TO THE NORTH OF
PANAMA...CONVECTION IS TO INTENSIFY TO 15-20MM/DAY AND MAXIMA OF
25-50MM ON FRIDAY TO SATURDAY. FURTHERMORE...THE NASCENT SURFACE
LOW IS TO ALSO FAVOR A MOIST WESTERLY FLOW ACROSS THE EASTERN
PACIFIC TO WESTERN COLOMBIA. IN RESPONSE...DIURNAL CONVECTION IS
TO INTENSIFY FROM 10-15MM/DAY AND MAXIMA OF 20-35MM EARLY IN THE
CYCLE TO 15-20MM/DAY AND MAXIMA OF 25-50MM DURING THE WEEKEND.

DAVISON/GALVEZ...WPC (USA)