Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6
000
FXCA20 KWBC 281811
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
211 PM EDT TUE JUL 28 2015

DISCUSSION FROM JUL 28/12 UTC: TUTT LOWS BOUND THE SOUTHERN
FRINGES OF A BROAD CELL OF THE SUBTROPICAL RIDGE OVER NORTH
AMERICA. UNDER THE STEERING FLOW OF THE RIDGE TO THE NORTH...ONE
IS TO PULL ACROSS BAJA PENINSULA EARLY IN THE CYCLE...THEN TO THE
WEST-NORTHWEST INTO THE EASTERN PACIFIC. MEANWHILE...THIS IS TO
ENHANCE CONVECTION ALONG THE SIERRA MADRE OCCIDENTAL...WHERE WE
EXPECT RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM IN
SCATTERED CONVECTION. ANOTHER LOW TO THE EAST LIES OVER SOUTHERN
MEXICO. THROUGH THIS EVENING THE LOW WILL MOVE SOUTH OF
GUERRERO...NEARING COLIMA/ NAYARIT LATER ON WEDNESDAY. THIS LOW IS
TO REMAIN CUT OFF FROM THE FLOW...AND AS SUCH IT IS EXPECTED TO
GRADUALLY WEAKEN/FILL AS IT MIGRATES FARTHER TO THE WEST. OVER THE
NEXT COUPLE OF DAYS THIS IS TO ENHANCE LATE AFTERNOON CONVECTION
OVER CENTRAL-SOUTHWEST MEXICO...WHERE WE EXPECT RAINFALL AMOUNTS
OF 05-10MM/DAY AND MAXIMA OF 15-25MM.

THERE IS ALSO AN UPPER LEVEL SHORT WAVE TROUGH OVER THE NORTHWEST
CARIBBEAN. THIS IS TO EVOLVE INTO A CLOSED LOW EARLY ON
THURSDAY...TO THEN MEANDER WEST INTO NORTHERN CENTRAL
AMERICA/CHIAPAS IN SOUTHERN MEXICO LATER IN THE DAY. AS IT
MEANDERS OVER THE WESTERN CARIBBEAN THE SHORT WAVE TROUGH/TUTT LOW
IS TO ENHANCE DIURNAL CONVECTION ACROSS HONDURAS-GUATEMALA...WITH
MOST ACTIVE ON WEDNESDAY-THURSDAY...WHEN WE EXPECT RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM.

MEANDERING MID LEVEL TROUGH OVER THE WESTERN ATLANTIC-FLORIDA
PENINSULA SEPARATES THE BROAD CONTINENTAL RIDGE FROM A CELL OF THE
SUBTROPICAL RIDGE OVER THE NORTHERN CARIBBEAN ISLANDS. AS THE
TROUGH PRESSES AGAINST THE RIDGE TO THE SOUTH EXPECTING SOME
EROSION EARLY ON THURSDAY MORNING...WITH SHORT WAVE TROUGH TO THEN
MOVE OVER THE NORTHWEST BAHAMAS. THIS WILL LEAD TO GRADUAL
INCREASE IN DEEP LAYER CONVECTIVE INSTABILITY...WITH THE
GALVEZ-DAVISON INDEX (GDI) SHOWING INCREASED RISK OF THUNDERSTORMS
ON THURSDAY TO FRIDAY. ACROSS GRAND BAHAMA-GREAT ABACO TO BIMINI
EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15MM
THROUGH THURSDAY MORNING. DURING THE DAY ON FRIDAY THIS INCREASES
TO 10-15MM/DAY AND MAXIMA OF 20-45MM.

AS MID LEVEL RIDGE IS TO REMAIN OVER THE NORTHERN CARIBBEAN
ISLES...FAIR WEATHER CONDITIONS ARE FORECAST TO PREVAIL THROUGH
THURSDAY EVENING. ALOFT...A TUTT LOW RETROGRESSES ACROSS THE
VIRGIN ISLES TO PUERTO RICO THROUGH WEDNESDAY...INTO HISPANIOLA ON
THURSDAY. ALTHOUGH WELL DEFINED AT UPPER LEVELS...THIS WILL NOT BE
STRONG ENOUGH TO OVERCOME NEGATIVE INFLUENCE OF MID LEVEL RIDGE
PATTERN. CONVECTIVE ENHANCEMENT WITH THIS TUTT WILL BE QUITE
LIMITED. AT LOW LEVELS THE UNFAVORABLE MID LEVEL CONDITIONS
COMBINE WITH SURGING EASTERLY TRADES AND ADVECTION OF A SAHARAN
AIR LAYER...THUS DECREASING CHANCES FOR CONVECTION THROUGH THE
SHORT RANGE PERIOD.

FARTHER EAST...ANOTHER TUTT LOW IS TO CLOSE NORTH OF FRENCH GUIANA
LATER ON THURSDAY...TO MEANDER WEST ALONG THE COAST OF THE GUIANAS
TO THE LESSER ANTILLES THROUGH FRIDAY EVENING/SATURDAY MORNING. AS
IT MEANDERS TO THE NORTH...POSITIVE INTERACTION WITH THE ATLANTIC
ITCZ IS TO SUSTAIN AN INCREASE IN CONVECTION LATER ON THURSDAY.
MEANWHILE...EXPECT RAINFALL AMOUNTS OF 00-05MM/DAY AND MAXIMA OF
10MM...INCREASING TO 05-10MM/DAY AND MAXIMA OF 15MM.

TROPICAL/EASTERLY WAVES INITIALIZED AT 12UTC
INITIAL  24     36     48     60     72     84     96        TYPE
51W      56W    61W    66W    70W    74W    78W    81W       TW
74W      79W    83W    85W    88W    91W    93W    96W     TW/SURGE
86W      90W    92W    95W    98W   101W   104W   107W       TW

TROPICAL WAVE IS INITIALIZED ALONG 51W AND SOUTH OF 22N. THIS IS
TO QUICKLY MOVE ACROSS THE GUIANAS...BUT UNDER INFLUENCE OF A DRY
SAHARAN AIR LAYER IT IS TO ONLY FAVOR RAINFALL AMOUNTS OF
00-05MM/DAY AND WIDELY ISOLATED MAXIMA OF 10MM. OVER THE ISLAND
CHAIN MOST ACTIVE IS EXPECTED ACROSS THE NORTHERN WINDWARD-FRENCH
ISLES ON WEDNESDAY...WITH RAINFALL AMOUNTS OF 00-05MM/DAY AND
MAXIMA OF 10MM...WITH SIMILAR AMOUNTS OVER THE VIRGIN ISLES-PUERTO
RICO ON FRIDAY MORNING. OVER NORTHEAST-CENTRAL VENEZUELA THIS IS
TO THEN FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF
15-20MM...WHILE OVER NORTHWEST VENEZUELA/NORTHERN COLOMBIA
EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM
EARLY ON FRIDAY MORNING.

TROPICAL WAVE ALONG 74W IS TO INTERACT WITH THE NEAR EQUATORIAL
TROUGH/ITCZ OVER COLOMBIA-PANAMA. OVER WESTERN COLOMBIA EXPECT
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-30MM...WHILE OVER
PANAMA-COSTA RICA-SOUTHERN NICARAGUA IT WILL FAVOR ACCUMULATION OF
05-10MM/DAY AND MAXIMA OF 15-20MM. ACROSS NORTHEAST NICARAGUA TO
HONDURAS...IN INTERACTION WITH DEEPENING TUTT LOW...EXPECT
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM ON WEDNESDAY
TO THURSDAY. SIMILAR AMOUNTS ARE EXPECTED OVER GUATEMALA-SOUTHERN
MEXICO ON THURSDAY TO FRIDAY. OVER CENTRAL-SOUTHWEST MEXICO THIS
INCREASES TO 10-15MM/DAY AND MAXIMA OF 20-35MM ON FRIDAY TO
SATURDAY MORNING.

TROPICAL WAVE ALONG 86W IS TO TRIGGER SCATTERED CONVECTION ACROSS
GUATEMALA-SOUTHERN MEXICO EARLY IN THE CYCLE...TO SUSTAIN RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM. AS IT MOVES ACROSS
SOUTHWEST MEXICO EARLY ON WEDNESDAY THIS IS TO THEN FAVOR RAINFALL
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 20-30MM LATER ON THURSDAY
THROUGH FRIDAY MORNING.

SALMON...MS (ANTIGUA AND BARBUDA)
SAMUEL...MDS (SURINAME)
DAVISON...WPC (USA)
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.