TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
224 PM EDT FRI JUL 09 2021

TROPICAL DISCUSSION FROM JUL 09/18 UTC: WEST OVER THE
DOMAIN...MODELS INITIALIZE A NARROW UPPER LEVEL TROUGH/SHEAR AXIS
THAT EXTENDS FROM SOUTH TEXAS...ACROSS COAHUILA TO SONORA/SOUTHERN
BAJA CALIFORNIA. THE TROUGH SPLITS THE SUBTROPICAL RIDGE IN TWO
CELLS...WITH ONE OVER THE SOUTHWEST USA AND THE OTHER OVER THE
GULF OF MEXICO. THE TROUGH ALOFT IS FORECAST TO GRADUALLY WEAKEN
AS IT MEANDERS WEST ACROSS THE NORTHERN STATES OF MEXICO THROUGH
THE WEEKEND/EARLY NEXT WEEK. INITIALLY MOST ACTIVE CONVECTION WITH
THIS FEATURE IS EXPECTED ALONG THE SIERRA MADRE ORIENTAL IN
NORTHEAST MEXICO WITH ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF
20-45MM. ON SATURDAY THIS SPREADS WESTWARD ACROSS THE NORTHERN
STATES OF MEXICO...AND ON SUNDAY THE FOCUS SHIFTS TO THE SIERRA
MADRE OCCIDENTAL AND DEL SUR WHILE THE MAXIMA INCREASES TO
25-50MM. FURTHERMORE...THIS IS TO ALSO TRIGGER ISOLATED TO
SCATTERED CONVECTION ACROSS SOUTHERN BAJA CALIFORNIA...WITH
ACCUMULATION OF 00-05MM/DAY AND MAXIMA OF 10MM. OTHER CONVECTION
IS EXPECTED TO THE SOUTH ACROSS THE SOUTHERN STATES OF MEXICO AND
NORTHERN CENTRAL AMERICA...WITH SEA BREEZE CONVECTION ACROSS THE
YUCATAN AND AIR MASS CONVECTION CLUSTERING ALONG THE CONTINENTAL
DIVIDE. INITIALLY THIS IS TO RESULT IN RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15-25MM...WITH ACTIVITY OVER THE YUCATAN
WEAKENING TO 00-05MM/DAY AND MAXIMA OF 10MM...WHILE OVER SOUTHERN
CHIAPAS-GUATEMALA/EL SALVADOR IT DECREASES TO 05-10MM/DAY AND
MAXIMA OF 15MM.

FARTHER EAST...OVER THE WESTERN ATLANTIC...A RETROGRESSING TUTT
LOW TO THE NORTH OF THE DOMINICAN REPUBLIC EXTENDS A SHORT WAVE
TROUGH TO THE SOUTH-SOUTHWEST TO THE SOUTHERN CARIBBEAN. THROUGH
SUNDAY MORNING THE TUTT LOW RETROGRESSES TO THE CENTRAL
BAHAMAS...WHILE THE SHORT WAVE TROUGH LINGERS OVER THE CENTRAL
CARIBBEAN. AT MID LEVELS THIS REFLECTS AS AN INVERTED TROUGH THAT
ALIGNS NEARLY VERTICALLY STACKED WITH THE UPPER LEVEL CIRCULATION.
BROAD RIDGE LIES TO THE EAST...WITH AXIS BRANCHING FROM THE
WESTERN ATLANTIC TO THE NORTHEAST CARIBBEAN...WHERE IT SUSTAINS A
TRADE WINDS INVERSION THAT IS INHIBITING ORGANIZED DEEP
CONVECTION. AT LOW LEVELS THIS COMBINES WITH STRONG EASTERLY
TRADES AND A SAHARAN AIR LAYER ENTRAINING FROM THE EAST IN SUPPORT
OF MOSTLY FAIR WEATHER CONDITIONS ACROSS THE NORTHEAST CARIBBEAN.
CONVECTION LIMIT TO A FEW STREAMERS FORMING OVER THE
LEEWARD/VIRGIN ISLES AND AIR MASS SHALLOW CONVECTION BUILDING OVER
WESTERN PUERTO RICO AND CENTRAL HISPANIOLA. AS THE UPPER LEVEL
TROUGH MEANDERS WEST TOWARDS THE BAHAMAS-CUBA...IT IS TO ENHANCE
THE DIURNAL PATTERN OVER THE ISLANDS...WITH RAINFALL AMOUNTS
INCREASING FROM 00-05MM/DAY AND MAXIMA OF 10MM DURING THE DAY
TODAY TO 05-10MM/DAY AND MAXIMA OF 15MM ON SUNDAY. HIGHER RAINFALL
AMOUNTS ARE EXPECTED TO THE SOUTH ALONG THE BASE OF THE UPPER
LEVEL TROUGH AND AN ATMOSPHERIC KELVIN WAVE PROPAGATING ACROSS THE
TROPICAL EASTERN PACIFIC. THESE INTERACTS WITH THE ITCZ/NEAR
EQUATORIAL TROUGH OVER NORTHERN SOUTH AMERICA AND SOUTHERN CENTRAL
AMERICA IN SUPPORT OF ORGANIZED DEEP CONVECTION. MOST INTENSE IS
TO AFFECT WESTERN COLOMBIA...WESTERN PANAMA...COSTA RICA AND
SOUTHERN NICARAGUA...WITH ACCUMULATION OF 20-40MM/DAY AND MAXIMA
OF 75-125MM DURING THE DAY TODAY. ON SATURDAY ACTIVITY ACROSS
WESTERN COLOMBIA WEAKENS TO 20-30MM/DAY AND MAXIMA OF
40-80MM...WHILE OVER COSTA RICA/SOUTHERN NICARAGUA THE MAXIMA
INCREASES TO 75-150MM.

TROPICAL WAVES/TUTT INDUCED PERTURBATIONS/TRADE WIND SURGES
INITIALIZED AT 12 UTC.
TYPE INIT  10/00 10/12 11/00 11/12 12/00 12/12 13/00 SOF
TW   34W   37W   39W   42W   45W   48W   51W   54W   12N
TW   46W   51W   56W   61W   66W   71W   76W   80W   22N
TW   68W   72W   75W   78W   81W   83W   86W   89W   11N
TW  105W  106W  108W  110W  112W  115W  117W  119W   19N

A TROPICAL WAVE ALONG 34W AND SOUTH OF 12N REACHES EASTERN FRENCH
GUIANA ON MONDAY MORNING...TO SUSTAIN MODERATE CONVECTION WITH
ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-25MM.

A PROGRESSIVE TROPICAL WAVE EXTENDS ALONG 46W TO 22N...WITH A
TRAILING TRADE WINDS SURGE/SAHARAN AIR LAYER CLEARLY EVIDENT IN
THE IMAGES. THE WAVE REACHES  AMAPA IN BRASIL/EASTERN FRENCH
GUIANA LATER TODAY. AS IT MAKES LANDFALL THE WAVE INTERACTS WITH
THE ATLANTIC ITCZ TO TRIGGER SCATTERED CONVECTION WITH RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-25MM. ON SATURDAY THIS
QUICKLY SPREADS ACROSS SURINAME TO GUYANA/NORTHEAST VENEZUELA
WHERE IT WILL SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA
OF 15-20MM. ACROSS THE ISLAND CHAIN TO THE EASTERN CARIBBEAN IT IS
TO THEN FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF
20-30MM. ACROSS PUERTO RICO IT WILL SUSTAIN RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15-20MM...WHILE OVER HISPANIOLA IT
INCREASES TO 10-15MM/DAY AND MAXIMA OF 20-35MM. ACROSS NORTHERN
VENEZUELA IT IS TO SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-20MM...WHILE TO THE SOUTH INTO EASTERN COLOMBIA IT
WILL RESULT IN RAINFALL AMOUNTS OF 15-20MM/DAY AND MAXIMA OF
25-50MM. ON SUNDAY THE FOCUS OF THE CONVECTION SHIFTS TO NORTHERN
AND WESTERN COLOMBIA...WHERE IT WILL SUPPORT RAINFALL AMOUNTS OF
15-20MM/DAY AND MAXIMA OF 40-80MM.

A TROPICAL WAVE ALONG 68W AND SOUTH OF 11N...IN INTERACTION WITH
THE NEAR EQUATORIAL TROUGH...WILL SUPPORT ORGANIZED CONVECTION
ACROSS VENEZUELA TO EASTERN COLOMBIA...WITH ACCUMULATION OF
15-20MM/DAY AND MAXIMA OF 25-50MM. OVER WESTERN COLOMBIA...IN
INTERACTION WITH A MEANDERING UPPER LEVEL TROUGH...THIS SURGES TO
20-40MM/DAY AND MAXIMA OF 75-125MM. ON SATURDAY EXPECTING
ADDITIONAL RAINFALL AMOUNTS OF 20-30MM/DAY AND MAXIMA OF 40-80MM
WHILE BUILDING WEST ACROSS PANAMA TO EASTERN COSTA RICA. THIS IS
TO THEN TRIGGER SIMILAR RAINFALL AMOUNTS ACROSS EASTERN NICARAGUA
ON SUNDAY WHILE OVER COSTA RICA EXPECTING ACCUMULATION OF
20-40MM/DAY AND MAXIMA OF 75-125MM.

A TROPICAL WAVE ALONG 105W AND SOUTH OF 19N ORIGINATES ON A
SURFACE LOW TO THE SOUTH/SOUTHWEST OF MEXICO. MOST ACTIVE
CONVECTION IS EXPECTED DURING THE DAY TODAY TO SUSTAIN RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 10MM ALONG THE COAST BETWEEN
GUERRERO AND NAYARIT...WHILE ALONG THE SOUTHERN SIERRA EXPECTING
MAXIMA OF 20-35MM. THIS WEAKENS ON SATURDAY AS THE WAVE PULLS AWAY.

DAVISON...WPC (USA)