TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
229 PM EDT WED MAY 15 2013

DISCUSSION FROM MAY 15/00UTC: AN AMPLIFYING MID/UPPER LEVEL TROUGH
IS INITIALIZED OVER THE WESTERN ATLANTIC TO THE BAHAMAS-CUBA. AS A
JET MAXIMA ROUNDS THE BASE OF THIS TROUGH...DIVERGENCE ON ITS
RIGHT ENTRANCE REGION IS ENHANCING CONVECTIVE DEVELOPMENT ACROSS
PORTIONS OF HISPANIOLA. THE UPPER TROUGH PROPAGATES ACROSS THE
NORTHEAST CARIBBEAN ISLANDS DURING THE DAY TODAY...WITH UPPER
DIVERGENCE SPREADING ACROSS PUERTO RICO-VIRGIN ISLES TO THE
LEEWARD ISLANDS. UPPER DIVERGENCE ACROSS PUERTO RICO-VI WEAKENS
THROUGH 42-48 HRS...WHILE OVER THE FRENCH-NORTHERN LEEWARD ISLANDS
IT IS EXPECTED TO PERSIST THROUGH 60-66 HRS

AT LOW LEVELS...A POLAR FRONT TRAILS TO THE WEST-SOUTHWEST ALONG
30N 60W...SOUTHEAST BAHAMAS TO CUBA. AHEAD OF THIS BOUNDARY...AN
INDUCED/PREFRONTAL TROUGH EXTENDS NORTH ACROSS PUERTO RICO TO THE
WESTERN ATLANTIC. THE TROUGH IS GOING TO BE SHORT LIVED...
WEAKENING EARLY IN THE FORECAST CYCLE. THIS FAVORS A MOIST
EAST-SOUTHEAST FLOW ACROSS THE LEEWARD ISLES/CARIBBEAN WATERS OF
PUERTO RICO...WITH MOISTURE CLUSTERING OFF THE CARIBBEAN COAST OF
HISPANIOLA. TRAILING END OF THE SURFACE FRONT REMAINS NEARLY
STATIONARY OVER THE SOUTHEAST BAHAMAS-CENTRAL/WESTERN CUBA THROUGH
36-48 HRS. BY 48-60 HRS IT WILL RETROGRESS INTO THE NORTHWEST
BAHAMAS WHERE IT IS EXPECTED TO QUICKLY DISSIPATE. AS THE FRONT
MEANDERS ACROSS THE BAHAMAS-CUBA IT IS TO TRIGGER ISOLATED TO
SCATTERED CONVECTION WITH RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15MM/DAY.

BUT AS THE SURFACE FRONT STALLS FAR TO THE NORTH...LIGHT TO
MODERATE EASTERLY TRADES ARE TO PERSIST ACROSS THE LEEWARD-VIRGIN
ISLES TO PUERTO RICO AND PORTIONS OF HISPANIOLA. MOIST PLUME IS TO
CLUSTER OVER THE NORTHEAST CARIBBEAN DURING THE NEXT COUPLE OF
DAYS WHILE EXTENDING BETWEEN THE FRENCH ISLES TO JUST SOUTH OF
HISPANIOLA. AT 60-72 HRS MOISTURE WILL SPREAD WEST INTO JAMAICA
WHILE IT STARTS TO EBB OVER THE NORTHEAST CARIBBEAN/LEEWARD
ISLANDS. ACROSS HISPANIOLA THIS IS TO FAVOR RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 20-35MM THROUGH 72 HRS. OVER PUERTO RICO
EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF
20-35MM...WITH MOST ACTIVE ALONG THE CORDILLERA AND WESTERN
INTERIOR PORTIONS OF THE ISLAND. THROUGH 72-96 HRS THIS WILL
DECREASE TO 05-10MM/DAY AND MAXIMA OF 15MM. OVER THE FRENCH
ISLANDS...UNDER FAVORABLE JET DYNAMICS...TRADE WINDS CONVERGENCE
IS TO FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF
20-35MM/DAY...WITH MAXIMA INCREASING TO 20-45MM BY 48-60 HRS.
THROUGH 72-84 HRS THIS WILL DECREASE TO 05-10MM/DAY AND MAXIMA OF
15MM/DAY. AS MOISTURE SPREADS ACROSS THE NORTHERN CARIBBEAN OVER
JAMAICA EXPECTING ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF
15MM...TO PEAK AT 20-35MM AT 48-72 HRS.

A 500 HPA HIGH OVER THE SOUTHERN GULF/CAMPECHE SOUND ANCHORS A MID
LEVEL RIDGE ACROSS CENTRAL-SOUTHERN MEXICO-CENTRAL AMERICA AND THE
WESTERN CARIBBEAN. AS PERTURBATIONS ON THE SOUTHERN STREAM LIFT
OVER THIS AXIS...RIDGE OVER THE GULF TENDS TO ERODE. OVER
MEXICO-CENTRAL AMERICA...HOWEVER...IT WILL TEND TO PERSIST THROUGH
AT LEAST 84-96 HRS. AS IT HOLDS...THE RIDGE IS TO CONTINUE
FAVORING A SUBSIDENCE CAP WHILE INHIBITING ORGANIZED DEEP
CONVECTION. HOWEVER...WIDELY SCATTERED LATE AFTERNOON CONVECTION
IS STILL POSSIBLE ALONG THE CONTINENTAL DIVIDE OVER SOUTHERN
GUATEMALA-HONDURAS/NORTHERN EL SALVADOR WHERE IT IS TO RESULT IN
LIGHT RAINFALL AMOUNTS.

OVER THE EASTERN PACIFIC...THE PANAMANIAN LOW CONTINUES TO
DOMINATE THE LOW LEVEL CIRCULATION OFF THE COAST OF COLOMBIA INTO
THE ANDEAN REGION. AS IT HOLDS...THE LOW ANCHORS THE ITCZ AS IT
ENTERS COLOMBIA OVER THE EJE CAFETERO. THE LOW REACHES MAXIMUM
INTENSITY EARLY IN THE CYCLE...AND THROUGH 42-48 HRS IT WILL START
TO MIGRATE WEST ALONG THE ITCZ INTO THE PACIFIC. BY 60-72 HRS THE
SURFACE LOW IS TO DISSIPATE/WEAKEN. AS IT PULLS AWAY THE ITCZ IS
TO MEANDER NORTH INTO THE AZUERO PENINSULA IN SOUTHERN PANAMA. THE
SURFACE LOW...AS IT MEANDERS OFF THE COAST OF COLOMBIA EARLY THIS
CYCLE...IS TO ENHANCE LOW LEVEL MOISTURE CONVERGENCE ALONG THE
COAST AND ANDEAN REGION INTO THE DARIEN IN EASTERN PANAMA. DURING
SHORT RANGE PERIOD THIS IS TO CONTINUE FAVORING GENERATION OF MESO
SCALE CONVECTIVE SYSTEMS. IN THIS AREA WE EXPECT RAINFALL AMOUNTS
OF 15-30MM/DAY AND MAXIMA OF 40-80MM/DAY. THIS IS TO THEN DECREASE
THROUGH 48-72 HRS TO 10-15MM/DAY AND MAXIMA OF 20-40MM. AS THE LOW
MODULATES THE ITCZ...ACROSS PANAMA EXPECTING LIGHT TO MODERATE
CONVECTION TO RESULT IN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA
OF 15-25MM. THIS SPREADS TO COSTA RICA BY 60-84 HRS...WITH
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM/DAY. OTHER
CONVECTION IS EXPECTED ACROSS EASTERN COLOMBIA TO NORTHEAST
VENEZUELA...WITH RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF
15-20MM/DAY.

NORTHERN SOUTH AMERICA IS UNDER INFLUENCE OF THE SUBEQUATORIAL
RIDGE...WITH AXIS TO MEANDER ACROSS NORTHERN BRASIL INTO THE
GUIANAS-VENEZUELA. RIDGE PATTERN HOLDS NEARLY UNCHANGED OVER THE
NEXT FEW DAYS. A CELL OF THE SUBTROPICAL RIDGE TO THE SOUTH...
HOWEVER...IS FORECAST TO STRENGTHEN THROUGH 60-72 HRS. AS THE
RIDGE BECOMES BETTER ORGANIZED IT WILL SUSTAIN A CROSS EQUATORIAL
TROUGH ACROSS NORTHEAST BRASIL INTO THE TROPICAL ATLANTIC. THE
UPPER TROUGH WILL INTERACT WITH THE ITCZ IN SUPPORT OF ORGANIZED
DEEP CONVECTION ACROSS NORTHERN FRENCH GUIANA TO SURINAME. IN THIS
AREA INITIALLY EXPECT RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA
OF 20-45MM. THROUGH 48-72 HRS THIS WILL DECREASE TO 05-10MM/DAY
AND MAXIMA OF 15-30MM. OVER NORTHERN GUYANA CONVECTION IS TO
INCREASE THROUGH 60-84 HRS. INITIALLY EXPECTING RAINFALL
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15MM...TO INCREASE TO
10-15MM/DAY AND MAXIMA OF 20-35MM.

BLENMAN...BMS (BARBADOS)
MCKENZIE...BDM (BAHAMAS)
DAVISON/GALVEZ...WPC (USA)