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)