TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
428 PM EDT THU SEP 12 2024

FORECAST BULLETIN 12 SEPT 2024 AT 2015 UTC:

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
DEPRESSION NINE-E...WHICH IS FORECAST TO BECOME A TROPICAL STORM
BY THIS EVENING. THIS TROPICAL CYCLONE IS EXPECTED TO MOVE OVER
THE SOUTHERN BAJA CALIFORNIA PENINSULA OVER THE NEXT FEW DAYS AND
CAUSE UP TO 200MM OF RAIN ACROSS THE SOUTHERN BAJA CALIFORNIA
PENINSULA AND AS MUCH AS 300MM OVER PORTIONS OF NORTHWESTERN
SINALOA OVER THE NEXT SEVERAL DAYS. PLEASE READ THE OFFICIAL
ADVISORIES FROM THE NATIONAL HURRICANE CENTER REGARDING THIS
TROPICAL CYCLONE...WHERE THERE ARE MORE DETAILS ON IT AS WELL AS A
RAINFALL FORECAST GRAPH.

ACROSS THE ATLANTIC BASIN...THERE ARE A FEW LOW PRESSURES ALONG
THE MONSOON TROUGH...WHICH ARE MOVING WEST. THE LOW PRESSURES ARE
VERY SMALL IN SIZE AND THE MODEL GUIDANCE INSISTS IN WEAKENING
THEM INTO A TROUGH AS THEY APPROACH THE LEEWARDS. HOWEVER...THE
LATEST SATELLITE IMAGERY CONTINUES TO SUGGEST CONVECTION AND
ROTATION ASSOCIATED WITH THESE LOW PRESSURES...PERSISTING LONGER
THAN THE GLOBAL MODELS ARE SUGGESTING. THAT BEING SAID...SINCE ALL
MODEL GUIDANCE HAS IT OPENING INTO A TROUGH...WE DECIDED TO KEEP
THAT AS A TROUGH IN OUR SURFACE FORECASTS...BUT THERE MAY BE
PERIODS OF SHOWERS AND THUNDERSTORMS FRIDAY INTO SATURDAY ACROSS
THE NORTHERN LEEWARDS AND PUERTO RICO.

AT THE SURFACE...OTHER THAN THE AFOREMENTIONED LOW PRESSURES ALONG
THE MONSOON TROUGH IN THE ATLANTIC...A BROAD HIGH PRESSURE ACROSS
THE NORTHEASTERN ATLANTIC AND A HIGH PRESSURE ENTERING THE
NORTHWESTERN ATLANTIC WILL CAUSE A PREVAILING EASTERLY TO
SOUTHEASTERLY WIND FLOW ACROSS THE TROPICAL ATLANTIC INTO THE
CARIBBEAN. THIS SOUTHEASTERLY WIND FLOW WILL PLAY A ROLE IN THE
LOCATION OF THE AFTERNOON CONVECTION THAT DEVELOPS EACH AFTERNOON
ACROSS PUERTO RICO AND HISPANIOLA.

IN THE MID LEVELS...THERE IS A WEAKENING LOW PRESSURE OVER THE
CENTRAL ATLANTIC...WHICH IS EXPECTED TO BE AN OPEN TROUGH BY THIS
EVENING. A BROAD HIGH PRESSURE IS LOCATED AND WILL PERSIST OVER
THE BAHAMAS INTO THE GULF OF MEXICO THROUGH FRIDAY. A WEAK MID
LEVEL TROUGH OVER NORTHWESTERN MEXICO WILL DEVELOP BY
FRIDAY...WHILE A MID LEVEL HIGH PRESSURE WILL PERSIST OVER CENTRAL
MEXICO OVER THE NEXT FEW DAYS.

THERE IS AN UPPER HIGH PRESSURE OVER CENTRAL MEXICO...THAT WILL
EXTEND EAST INTO THE GULF OF MEXICO. ANOTHER UPPER HIGH PRESSURE
IS ALSO LOCATED ACROSS THE CENTRAL TO EASTERN TROPICAL ATLANTIC.
THIS GENERAL PATTERN COULD PROMOTE SOME STABILITY OR AT LEAST KEEP
DEEP VERTICAL DEVELOPMENT FROM OCCURRING...CONSIDERING THAT THE
LOW LEVELS HAVE ENOUGH MOISTURE AND THAT THERE IS A POTENTIAL SFC
TROUGH MOVING INTO THE LEEWARDS AND PR/USVI ON FRIDAY INTO
SATURDAY...SIGNIFICANT RAIN COULD STILL OCCUR.

THE AREA WITH HIGHEST RAINFALL POTENTIAL OVER THE NEXT THREE DAYS
WILL BE PORTIONS OF WESTERN MEXICO AND THE SOUTHERN BAJA PENINSULA
DUE TO THE CURRENT TROPICAL DEPRESSION NINE-E. THE MODEL GUIDANCE
HAD BEEN A BIT SHY OVER THE PAST FEW DAYS WITH THE RAINFALL
SOLUTION...BUT THAT IS NO LONGER THE CASE. THERE IS PRETTY GOOD
AGREEMENT WITH THE RAINFALL TOTALS OVER THE AREA REGARDING THE
TROPICAL CYCLONE. HOWEVER...THE MODEL GUIDANCE SEEMS TO BE GREATLY
UNDERESTIMATING THE RAINFALL OVER THE SOUTHERN SECTIONS OF CENTRAL
AMERICA. THE LATEST SATELLITE IMAGERY SHOWS A STRONG AREA OF
CONVECTION OVER PANAMA AND COSTA RICA...AND A SIMILAR DISCREPANCY
HAS BEEN OBSERVED OVER THE CARIBBEAN ISLANDS. FOR THAT
REASON...THE RAINFALL FORECAST OVER SOUTHERN CENTRAL AMERICA AND
THE CARIBBEAN IS A BIT HIGHER THAN WHAT THE MODEL GUIDANCE IS
SUGGESTING.


ALAMO...(WPC)

NOTE...THE NEXT DISCUSSION IS SCHEDULED FOR MONDAY 16 SEPTEMBER
2024.