762  
FXCA20 KWBC 221837  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
236 PM EDT FRI SEP 22 2017  
 
AT 15 UTC HURRICANE MARIA CENTERED NEAR 22.8N 71.2W...WITH MAXIMUM  
SUSTAINED WINDS OF 110KT AND CENTRAL PRESSURE OF 959 HPA. THE  
HURRICANE IS MOVING TO THE NORTH-NORTHWEST AT 08KT. SEE NHC  
BULLETIN FOR DETAILS.  
 
TROPICAL DISCUSSION FROM SEP 22/12 UTC: AT 200 HPA...A CLOSED HIGH  
NEAR 20N 100W EXTENDS A RIDGE NORTH ACROSS MEXICO TO THE WESTERN  
USA. THE HIGH AMPLITUDE RIDGE IS EXPECTED TO HOLD DURING THE NEXT  
FEW DAYS. DOWNSTREAM FROM THIS AXIS...A TROUGH IS TO RAPIDLY  
AMPLIFY ACROSS THE SOUTHEAST USA TO THE EASTERN GULF-YUCATAN  
PENINSULA LATER TODAY. THE TROUGH BOTTOMS OUT OVER SOUTHERN  
MEXICO/GUATEMALA ON FRIDAY-SATURDAY. THE HIGH AMPLITUDE RIDGE IS  
VENTING DEEP CONVECTION IN ASSOCIATION WITH AN AREA OF DISTURBED  
WEATHER OFF THE SOUTHWEST COAST OF MEXICO. TROPICAL WAVE STREAMING  
ACROSS CENTRAL MEXICO WILL MERGE WITH THIS DISTURBANCE TO LIKELY  
FAVOR GENERATION OF A TROPICAL CYCLONE. NOTE THAT THE NHC HAS A  
HIGH RISK AREA OF TROPICAL CYCLONE FORMATION OVER THE NEXT FEW  
DAYS. MEANWHILE...THE DISTURBANCE IS TO FAVOR COASTAL CONVECTION  
BETWEEN GUERRERO AND COLIMA/NAYARIT. IN THIS AREA EXPECTING  
RAINFALL AMOUNTS OF 20-40MM/DAY AND MAXIMA OF 50-100MM/DAY DURING  
THE NEXT TWO DAYS. ON SUNDAY FOCUS OF THE HEAVY CONVECTION SHIFTS  
TO SOUTHERN SINALOA-COLIMA WITH ACCUMULATION OF 15-20MM/DAY AND  
MAXIMA OF 35-70MM. OVER NORTHWEST MEXICO...ALONG THE CONTINENTAL  
DIVIDE...DIURNAL CONVECTION WILL RESULT IN RAINFALL AMOUNTS OF  
00-05MM/DAY AND MAXIMA OF 10MM. ON SATURDAY IT INCREASES TO  
05-10MM/DAY AND MAXIMA OF 15-25MM. ON SATURDAY-SUNDAY FOCUS OF THE  
CONVECTION SHIFTS EAST ACROSS COAHUILA-CHIHUAHUA WITH ACCUMULATION  
OF 10-15MM/DAY AND MAXIMA OF 20-35MM. ON THE CENTRAL STATES OF  
MEXICO EXPECTING ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF  
15-20MM.  
 
AS THE UPPER LEVEL TROUGH AMPLIFIES ACROSS THE YUCATAN  
PENINSULA...THIS IS TO ENHANCE DIURNAL CONVECTION ACROSS SOUTHERN  
MEXICO-NORTHERN GUATEMALA-BELIZE...TO FAVOR RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-25MM. HIGHER AMOUNTS ARE EXPECTED  
ALONG THE PACIFIC COAST BETWEEN SOUTHERN  
CHIAPAS/GUATEMALA-SOUTHERN HONDURAS/EL SALVADOR TO NORTHWEST  
NICARAGUA...WHERE IN INTERACTION WITH THE EASTERN PACIFIC ITCZ  
EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM.  
ON SATURDAY-SUNDAY CONDITIONS APPEAR FAVORABLE FOR AN MCS TO FORM  
OVER THE GULF OF FONSECA...TO AFFECT EL SALVADOR-SOUTHWEST  
HONDURAS AND NORTHWEST NICARAGUA. THIS WILL RESULT IN RAINFALL  
AMOUNTS OF 15-30MM/DAY AND MAXIMA OF 40-80MM. LESSER AMOUNTS ARE  
EXPECTED TO THE NORTH OVER HONDURAS AND ACROSS EASTERN  
NICARAGUA...WITH RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF  
15-25MM. ACROSS SOUTHERN NICARAGUA-COSTA RICA TO PANAMA EXPECTING  
ITCZ RELATED CONVERGENCE TO RESULT IN RAINFALL AMOUNTS OF  
10-15MM/DAY AND MAXIMA OF 20-35MM. THROUGH SUNDAY THIS IS TO  
INTENSIFY...TO SUSTAIN RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA  
OF 30-60MM. THE DEEP UPPER LEVEL TROUGH IS TO ALSO VENT DIURNAL  
CONVECTION ACROSS CUBA AND THE BAHAMAS. ACROSS CUBA INITIALLY  
EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-40MM.  
ON SATURDAY AND SUNDAY IT IS TO THEN FAVOR RAINFALL AMOUNTS OF  
05-10MM/DAY AND MAXIMA OF 15-25MM. OVER THE NORTHWEST BAHAMAS  
EXPECTING RAINFALL ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF  
15-25MM/DAY. HIGHER AMOUNTS ARE EXPECTED TO THE SOUTH EARLY IN THE  
CYCLE UNDER THE INFLUENCE OF HURRICANE MARIA (SEE BELOW FOR  
DETAILS).  
 
DOWNSTREAM FROM THE UPPER LEVEL TROUGH...BROAD RIDGE EXTENDS FROM  
THE EASTERN CARIBBEAN NORTH INTO THE WESTERN ATLANTIC. AT 500 HPA  
A WEAK RIDGE IS INITIALIZED NORTH OF VENEZUELA. THE MID LEVEL  
RIDGE IS FORECAST TO BUILD NORTH ACROSS THE GREATER ANTILLES AND  
WEST TO THE CENTRAL CARIBBEAN. AS THE RIDGE BUILDS IT IS TO  
DISPLACE HURRICANE MARIA TO THE NORTH. EARLY IN THE CYCLE THIS IS  
TO SUSTAIN ORGANIZED CONVECTION ACROSS THE TURKS/SOUTHEAST  
BAHAMAS...WITH RAINFALL AMOUNTS OF 50-100MM/DAY AND MAXIMA OF  
200-250MM. OVER THE CENTRAL BAHAMAS IT IS TO FAVOR RAINFALL  
AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 35-70MM. FURTHERMORE...OVER  
THE EASTERN CARIBBEAN THE DEEP CYCLONE SUSTAINS A LONG FETCH  
SOUTHERLY FLOW. THIS IS TO PERSIST DURING THE NEXT FEW DAYS...WITH  
FLOW GRADUALLY BACKING TO THE SOUTHEAST LATER DURING THE WEEKEND.  
MEANWHILE...THIS FLOW WILL ENHANCE THE TRANSPORT OF DEEP TROPICAL  
MOISTURE ACROSS THE EASTERN CARIBBEAN TO SOUTHERN  
HISPANIOLA-PUERTO RICO. ACROSS SOUTHERN HISPANIOLA IT IS TO RESULT  
IN RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF 25-50MM. A LULL  
IN ACTIVITY IS EXPECTED ON SATURDAY WHEN THE DAILY MAXIMA PEAKS AT  
15-25MM...BUT ON SUNDAY INCREASES AGAIN TO 25-50MM. ACROSS PUERTO  
RICO THIS WILL COMBINE WITH FEEDER BAND CONVERGENCE EARLY IN THE  
CYCLE TO TRIGGER RAINFALL AMOUNTS OF 25-50MM/DAY AND MAXIMA OF  
75-125MM. ON SATURDAY-SUNDAY IT IS TO FAVOR RAINFALL AMOUNTS OF  
15-20MM/DAY AND MAXIMA OF 35-70MM...WHILE ON SUNDAY IT DECREASES  
TO 00-05MM/DAY AND MAXIMA OF 20MM.  
 
A TUTT TO THE EAST OF THE EASTERN CARIBBEAN RIDGE LIES ALONG  
53W/54W TO THE GUIANAS. THE TROUGH IS TO HOLD DURING THE NEXT FEW  
DAYS. OVER NORTHERN FRENCH GUIANA-SURINAME THIS IS TO FAVOR  
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM ON  
SATURDAY-SUNDAY. HIGHER AMOUNTS ARE EXPECTED ACROSS THE ORINOCO  
DELTA REGION IN NORTHEAST VENEZUELA-TRINIDAD/TOBAGO AND NORTHERN  
GUYANA...WHERE IN INTERACTION WITH THE ATLANTIC ITCZ EXPECTING  
RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-35MM. ACROSS  
CENTRAL-WESTERN VENEZUELA AND SOUTHERN COLOMBIA DIURNAL CONVECTION  
WILL SUSTAIN RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF  
20-30MM. ON SATURDAY THIS INCREASES TO 10-15MM/DAY AND MAXIMA OF  
20-45MM. OVER NORTHERN COLOMBIA AND VENEZUELA EXPECT RAINFALL  
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM. HIGHER AMOUNTS ARE  
EXPECTED OVER WESTERN COLOMBIA...WHERE THE PANAMANIAN TROUGH IS TO  
SUSTAIN A MOIST WESTERLY FLOW. THIS WILL RESULT IN RAINFALL  
AMOUNTS OF 05-10MMD/AY AND MAXIMA OF 15-25MM. THROUGH SUNDAY THIS  
INCREASES TO 15-20MM/DAY AND MAXIMA OF 30-60MM.  
 
TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC:  
INITIAL 24 36 48 60 72 84 96 TYPE SOF  
43W 46W 49W 53W 57W 60W 63W 66W TW 22N  
53W 55W 57W DISSIPATES TW 17N  
102W DISSIPATES TW 22N  
 
TROPICAL WAVE ALONG 43W AND SOUTH OF 22N IS TO CONFINE TO THE  
ATLANTIC ITCZ DURING THE NEXT DAY OR SO. THIS WAVE IS ACCOMPANIED  
BY A TRADE WINDS SURGE AND A DUSTY SAHARAN AIR LAYER. ON SATURDAY  
IT MOVES NORTH OF THE GUIANAS...WHERE IT WILL TRIGER RAINFALL  
AMOUNTS OF 05-10MM/DAY AND ISOLATED MAXIMA OF 15-20MM ALONG THE  
NORTH COAST. AHEAD OF THE WAVE...TRADE WIND CONVERGENCE WILL ALSO  
STIMULATE ACTIVITY ACROSS TRINIDAD AND TOBAGO THROUGH EXTREME  
NORTHERN GUYANA...TO PRODUCE RAINFALL AMOUNTS OF 15-20MM/DAY AND  
MAXIMA OF 25-50MM ON SUNDAY. ON THE LEEWARD ISLES EXPECTING  
ACCUMULATION OF 00-05MM/DAY AND MAXIMA OF 10MM. ON MONDAY...DRY  
AIR IS TO RAPIDLY ENTRAIN ACROSS THE EASTERN CARIBBEAN ISLES.  
 
A TROPICAL WAVE ALONG 53W AND SOUTH OF 17N IS TO WEAKEN AS IT  
MOVES TO THE CONVERGENT SIDE OF THE UPPER LEVEL TUTT EAST OF THE  
ISLANDS. CONVECTION WITH THIS FEATURE WILL LIMIT TO THE ITCZ AND  
NORTHWARD.  
 
TROPICAL WAVE ALONG 102W AND SOUTH OF 22N MERGES INTO NASCENT  
TROPICAL DISTURBANCE OFF THE COAST OF MEXICO. MEANWHILE...THIS IS  
TO FAVOR SCATTERED COASTAL CONVECTION BETWEEN GUERRERO TO  
COLIMA/NAYARIT...WITH ACCUMULATION OF 20-40MM/DAY AND MAXIMA OF  
50-100MM.  
 
GUY...NMS (BELIZE)  
RIVAS...SENAMHI (PERU)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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