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Tropical Discussion
 
(Latest Discussion - Issued 1513Z Sep 18, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1113 AM EDT FRI SEP 18 2020

AT 15 UTC...HURRICANE TEDDY CENTERED NEAR 22.1N 56.1W. MINIMUM
CENTRAL PRESSURE WAS 947 HPA AND MAXIMUM SUSTAINED WINDS 115KT
WITH GUSTS UP TO 140KT. TEDDY WAS MOVING TO THE NORTHWEST OR AT
315 DEGREES AND AT 10KT.

ST 15 UTC...TROPICAL DEPRESSION TWENTY TWO CENTERED NEAR 23.8N
93.9W. MINIMUM CENTRAL PRESSURE WAS ESTIMATED AT 1005
HPA...MAXIMUM SUSTAINED WINDS AT 30KT WITH GUSTS UP TO 40KT.
TWENTY TWO WAS MOVING TO THE NORTH-NORTHEAST OR AT 15 DEGREES AND
AT 06 KT.

TROPICAL DISCUSSION FROM SEPTEMBER 18/18 UTC: IN THE UPPER
LEVELS...A POLAR TROUGH IS MEANDERING EASTWARD ACROSS NORTHEAST
MEXICO. THIS IS ENHANCING CONVECTION IN THE REGION...BUT IS ALSO
ASSOCIATED WITH DRY NORTHWESTERLY FLOW IN AREAS WESTWARD. THIS
WILL SUSTAIN A DRYING TREND IN NORTHERN AND CENTRAL MEXICO THROUGH
THE WEEKEND AND INTO EARLY NEXT WEEK. CONVERSELY...AREAS TO THE
SOUTH OF 20N WILL REMAIN ACTIVE THROUGH THE CYCLE UNDER THE
INFLUENCE OF A TROPICAL WAVE....AND TROPICAL DEPRESSION TWENTY
TWO. THE LATTER WILL CONTINUE ENHANCING ONSHORE FLOW ALONG THE
GULF COAST OF MEXICO THROUGH THE CYCLE...TO SUSTAIN MODERATE
PRECIPITATION. IN TERMS OF ACCUMULATIONS...ON FRIDAY...EXPECTING
15-20MM/DAY AND MAXIMA OF 25-50MM IN THE YUCATAN PENINSULA AND IN
ALL AREAS TO THE SOUTH OF 20N. IN NORTHEAST MEXICO...EXPECTING
05-10MM/DAY AND MAXIMA OF 15-25MM. ON SATURDAY...LARGEST AMOUNTS
ARE EXPECTED IN TABASCO AND CHIAPAS WHERE ONSHORE FLOW FROM THE
GULF OF MEXICO WILL FAVOR 15-20MM/DAY AND MAXIMA OF 30-60MM. TO
THE WEST...EXPECTING 10-15MM/DAY AND MAXIMA OF 20-40MM IN AREAS TO
THE SOUTH OF 20N AND IN NAYARIT/JALISCO. IN THE YUCATAN PENINSULA
EXPECTING 10-15MM/DAY AND MAXIMA OF 20-35MM. ON SUNDAY...LARGEST
ACCUMULATIONS WILL CLUSTER IN CHIAPAS...TABASCO AND SOUTHERN
VERACRUZ...WHERE EXPECTING 10-15MM/DAY AND MAXIMA OF 20-45MM. IN
THE YUCATAN PENINSULA EXPECTING 05-10MM/DAY AND MAXIMA OF 15-25MM.
SIMILAR AMOUNTS ARE EXPECTED IN SOUTHWEST MEXICO.

TO THE EAST...A ROBUST AND LARGE UPPER RIDGE CENTERS OVER THE
NORTHWEST BAHAMAS AND EXTENDS ZONALLY FROM THE WESTERN GULF OF
MEXITO INTO 70W. A TUTT LIES TO THE EAST...CURRENTLY LOCATED TO
THE NORTH OF PUERTO RICO AT 23N 64W. THROUGH SUNDAY...THE RIDGE IS
FORECAST TO HOLD BUT GRADUALLY WEAKEN UNDER THE PRESSURE OF A
LARGE AND ROBUST POLAR TROUGH TO THE NORTH...WHILE THE TUTT
WEAKENS AS IT MEANDERS JUST TO THE NORTH OF HISPANIOLA AND PUERTO
RICO. AS THE RIDGE AND UPPER TROUGH WEAKEN...THIS WILL RESULT IN A
DECREASED INFLUENCE OF THE UPPER PATTERN ON RAINFALL
ACCUMULATIONS. IN THE LOW-LEVELS...PRECIPITATION WILL ORGANIZED
WITH SURFACE TROUGHS INDUCED BY HURRICANE TEDDY...BY THE
ITCZ...FORECAST TO MEANDER INTO THE FRENCH ANTILLES BY
SUNDAY...AND BY A SURFACE FRONT INDUCED BY THE AFOREMENTIONED
POLAR TROUGH. ON THE POSITIONS OF THE SURFACE FRONT...ON FRIDAY
EVENING IT IS FORECAST TO EXTEND ALONG NORTHERN FLORIDA INTO THE
NORTHWEST GULF OF MEXICO. BY SATURDAY EVENING IT IS FORECAST TO
EXTEND ACROSS NORTH-CENTRAL FLORIDA...WHILE A PRE-FRONTAL TROUGH
STRUCTURE DEVELOPS OVER THE NORTHWEST BAHAMAS...TO FAVOR
05-10MM/DAY AND ISOLATED MAXIMA OF 15-20MM. ON SUNDAY...THE COLD
FRONT WILL MAKE IT INTO THE NORTHWEST BAHAMAS...TO TRIGGER
SCATTERED THUNDERSTORMS WITH ACCUMULATION OF 05-10MM/DAY AND
MAXIMA OF 15-25MM.

ON RAINFALL ACCUMULATIONS IN THE REST OF THE CARIBBEAN...ON
FRIDAY...LARGEST ACCUMULATIONS WILL DEVELOP IN THE WINDWARD
ISLANDS IN ASSOCIATION WITH THE ITCZ MODULATED NORTHWARD BY TEDDY.
EXPECTING 10-15MM/DAY AND SCATTERED MAXIMA OF 20-35MM. A TROUGH IN
ASSOCIATION WITH TEDDY WILL SUSTAIN 05-10MM/DAY AND MAXIMA OF 15MM
IN THE CENTRAL LESSER ANTILLES. SIMILAR AMOUNTS ARE EXPECTED IN
PUERTO RICO AND THE EASTERN DOMINICAN REPUBLIC IN DIURNAL
CONVECTION...WHILE IN WESTERN HISPANIOLA AND IN CUBA EXPECTING
05-10MM/DAY AND MAXIMA OF 15-20MM. ON SATURDAY...THE LARGEST
ACCUMULATIONS ARE EXPECTED IN THE NORTHERN WINDWARD ISLANDS AND
FRENCH ANTILLES IN ASSOCIATION WITH THE ITCZ...TO REACH
10-15MM/DAY AND MAXIMA OF 20-35MM. IN THE LEEWARD ISLANDS...A
TROUGH ASSOCIATED WITH TEDDY WILL FAVOR 05-10MM/DAY AND MAXIMA OF
15MM. IN PUERTO RICO AND THE DOMINICAN REPUBLIC...DIURNAL
CONVECTION WILL FAVOR 05-10MM/DAY AND MAXIMA OF 15-25MM...WHILE IN
CENTRAL AND WESTERN CUBA EXPECTING 05-10MM/DAY AND MAXIMA OF
15-20MM. ON SUNDAY...ITCZ CONVECTION IN THE FRENCH ANTILLES AND
SOUTHERN LEEWARD ISLANDS WILL FAVOR 05-10MM/DAY AND MAXIMA OF
15-20MM. DIURNAL CONVECTION IN HISPANIOLA...SOUTHEAST CUBA AND
WESTERN CUBA WILL FAVOR 05-10MM/DAY AND MAXIMA OF 15-25MM.

IN NORTHERN CENTRAL AMERICA...EXPECTING A GRADUAL DECREASE IN
ACCUMULATIONS AS A DRY AIR MASS ARRIVES FROM THE CARIBBEAN. ON
FRIDAY...LARGEST ACCUMULATIONS WILL CLUSTER FROM WESTERN HONDURAS
INTO GUATEMALA AND NORTHERN EL SALVADOR...WHERE DIURNAL CONVECTION
WILL SUSTAIN 15-20MM/DAY AND ISOLATED MAXIMA OF 25-50MM. THIS
DECREASES TO 10-15MM/DAY AND MAXIMA OF 20-35MM ON SATURDAY. ON
SUNDAY...A TUTT IS FORECAST TO DEVELOP OVER THE GULF OF HONDURAS.
THIS...IN COMBINATION WITH A TROUGH INDUCED BY HURRICANE TWENTY
TWO...WILL ENHANCE CONVECTION IN GUATEMALA AND WESTERN
HONDURAS/WESTERN EL SALVADOR TO FAVOR 10-15MM/DAY AND ISOLATED
MAXIMA OF 20-45MM.

IN SOUTHERN CENTRAL AMERICA...EXPECT A GRADUAL INCREASE IN DIURNAL
ACCUMULATIONS AS A MOIST AIR MASS ARRIVES FROM NORTHERN SOUTH
AMERICA. INITIALLY...EXPECTING 10-15MM/DAY AND MAXIMA OF 20-35MM
IN PANAMA AND SOUTHERN/WESTERN COSTA RICA. THIS GRADUALLY
INCREASES TO 15-20MM/DAY AND MAXIMA OF 25-50MM BY SUNDAY INTO
EARLY MONDAY.

CONVECTION IN NORTHERN SOUTH AMERICA WILL BE THE MOST ACTIVE ALONG
THE NET...AND IN COLOMBIA...WHERE ENHANCED WESTERLY FLOW ALONG THE
PACIFIC BASIN WILL SUSTAIN A CONTINUED MOISTURE INFLOW INTO THE
REGION. ON FRIDAY...THE LARGEST ACCUMULATIONS ARE EXPECTED IN
WESTERN...CENTRAL AND NORTHERN COLOMBIA...AND IN WESTERN
VENEZUELA...WHERE DIURNAL CONVECTION WILL FAVOR 10-15MM/DAY AND
MAXIMA OF 20-40MM. IN EASTERN VENEZUELA AND WESTERN GUYANA
EXPECTING 10-15MM/DAY AND MAXIMA OF 20-35MM. ON
SATURDAY...EXPECTING A PEAK IN ACTIVITY IN CENTRAL AND NORTHERN
COLOMBIA...AS WELL AS WESTERN VENEZUELA...WHERE EXPECTING
15-20MM/DAY AND MAXIMA OF 35-70MM. IN CENTRAL AND NORTHERN
VENEZUELA EXPECTING 10-15MM/DAY AND MAXIMA OF 20-35MM. IN
SOUTHWEST COLOMBIA...ONSHORE FLOW WILL FAVOR 10-15MM/DAY AND
MAXIMA OF 20-40MM. ON SUNDAY...LARGEST AMOUNTS ARE EXPECTED IN
NORTHERN COLOMBIA AND WESTERN VENEZUELA IN ASSOCIATION WITH THE
NET...TO REACH 15-20MM/DAY AND MAXIMA OF 25-50MM. IN WESTERN
COLOMBIA EXPECTING 10-15MM/DAY AND MAXIMA OF 20-35MM...WHILE IN
CENTRAL VENEZUELA EXPECTING 05-10MM/DAY AND MAXIMA OF 15-25MM.

TROPICAL WAVES/TUTT INDUCED PERTURBATIONS/TRADE WIND SURGES
TYPE  18/12  19/00  19/12  20/00  20/12  21/00  21/12  22/00  SOF
TW      94W    98W   101W   104W   106W   108W   110W   113W  22N
TW     107W   109W   111W   113W   116W   EXITS  ----   ----  25N

A TROPICAL WAVE IS PROPAGATING ACROSS SOUTHERN
MEXICO...INITIALIZED AT 94W AND TO THE SOUTH OF 22N. AS IT
PROPAGATES ACROSS SOUTHER MEXICO...IT WILL FAVOR 15-20MM/DAY AND
MAXIMA OF 25-50MM ON FRIDAY AND 10-15MM/DAY AND MAXIMA OF 20-40MN
ON SATURDAY...TO THEN EXIT INTO THE EASTERN PACIFIC WITH LIMITED
EFFECTS ON CONTINENTAL CONVECTION.

ANOTHER TROPICAL WAVE IS INITIALIZED AT 107W AND TO THE SOUTH OF
25N...AND IS HAVING LIMITED EFFECTS ON CONTINENTAL CONVECTION.

GALVEZ/DAVISON...WPC (USA)