947
FXHW01 KWNH 210856
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
456 AM EDT MON SEP 21 2026
VALID 00Z TUE 22 SEP 2026 - 00Z TUE 29 SEP 2026
...HEAVY RAIN AND FLOODING POTENTIAL NEXT WEEK WITH T.D. 15-E
REMNANTS...
ABOVE AVERAGE MOISTURE ALONG WITH BROAD, WEAK ENERGY ALOFT WILL
LINGER INTO THE EARLY PART OF THE WEEK. THIS COMBINATION SHOULD
LEAD TO SCATTERED SHOWERS WHICH CONTAIN LOCALLY HEAVY
RAINFALL...ESPECIALLY IN WINDWARD/MAUKA AREAS UNDER TYPICAL
MODERATE TRADES.
A BIGGER CONCERN FOR HEAVY RAINFALL IS THE APPROACH OF WHAT WAS
ONCE TROPICAL DEPRESSION 15E. IT WAS STILL FORECAST TO BE
APPROACHING HAWAII BY MID- TO LATE-WEEK. BY THAT TIME, DEEPER
MOISTURE LOOKS TO GET DRAWN NORTHWARD IN RESPONSE TO A SOUTHWARD
DIGGING TROUGH NORTHWEST OF HAWAII. MODEL GUIDANCE REMAINS VARIED
IN TERMS OF HOW MUCH IMPACT THE FORMER-15E HAS ON THE ISLAND IN
TERMS OF WIND AND RAIN...WHICH WILL DEPEND (IN PART) ON WHETHER
15-E CAN STRENGTHEN BACK INTO A TROPICAL CYCLONE. MULTIPLE
DETERMINISTIC ECMWF RUNS AND THE EC ENSEMBLE SPREAD IT ACROSS MUCH
OF THE STATE, WHILE THE RECENT EC-AIFS AND GFS KEEP IT SOUTH WITH
IMPACTS MORE LIMITED TO THE BIG ISLAND. AS OF LATE SUNDAY
NIGHT...CHANCES FOR TROPICAL CYCLONE FORMATION WAS NOT EXPECTED
FOR AT LEAST 48 HOURS (LATE TUESDAY/EARLY WEDNESDAY) AT THE
EARLIEST.
AS A RESULT...HEAVY TO EXCESSIVE RAINFALL IS POSSIBLE AND
FLOODING WILL BE A CONCERN, AT LEAST FOR THE BIG ISLAND. STAY
TUNED FOR FORECAST UPDATES ON THE DETAILS. THE HIGHER MOISTURE
VALUES LOOK TO CLEAR OUT NEXT WEEKEND.
BANN
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