433
FXHW01 KWNH 200954
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
554 AM EDT SUN SEP 20 2026
VALID 00Z MON 21 SEP 2026 - 00Z MON 28 SEP 2026
...HEAVY RAIN AND FLOODING POTENTIAL NEXT WEEK WITH T.D. 15-E
REMNANTS...
ABOVE AVERAGE MOISTURE (PRECIPITABLE WATER VALUES) ARE FORECAST
TO LINGER FOR SUNDAY AND MONDAY, ALONG WITH WEAK ENERGY ALOFT.
NOTHING LOOKS TOO ORGANIZED IN TERMS OF HEAVY RAINFALL, BUT
SCATTERED SHOWERS THAT DO OCCUR COULD CONTAIN ISOLATED HEAVY RAIN.
SHOWERS COULD FOCUS IN WINDWARD/MAUKA AREAS UNDER TYPICAL
MODERATE TRADES. BY LATE MONDAY OR TUESDAY, A WEAK TROUGH WITH
ENHANCED MOISTURE COULD TRACK WEST ACROSS THE STATE.
A TROPICAL DISTURBANCE WHICH WAS FORMERLY T.D. 15-E IS FORECAST TO
APPROACH HAWAII FROM THE SOUTHEAST AROUND TUESDAY. MEANWHILE A
TROUGH NORTHWEST OF HAWAII IS FORECAST TO DIG SOUTHWARD. THIS
COMBINATION WILL INCREASE MOISTURE (PWS TO 2.5 INCHES) AND
INSTABILITY FURTHER IN RESPONSE. MODELS VARY REGARDING WHERE/HOW
FAR NORTH THE ENHANCED MOISTURE/INSTABILITY WILL BE LOCATED.
MULTIPLE DETERMINISTIC ECMWF RUNS AND THE EC ENSEMBLE SPREAD THESE
ACROSS THE STATE, WHILE THE RECENT EC-AIFS AND GFS KEEP IT SOUTH,
MORE LIMITED TO THE BIG ISLAND. ANOTHER FACTOR IS THE POTENTIAL
FOR T.D. 15-E TO REDEVELOP INTO A TROPICAL CYCLONE. NHC IS KEEPING
AN EYE ON IT AND MODELS/ENSEMBLES/DEEPMIND MEMBERS DO SHOW THE
POTENTIAL FOR THIS. THE BEST CONSENSUS SEEMS TO SHOW THE CORE OF
THE LOW ITSELF STAYING SOUTH OF THE BIG ISLAND, BUT THE ECMWF IS
THE CLOSEST AND HENCE SHOWS THE HIGHER MOISTURE ANOMALIES ACROSS
THE STATE. 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.
TATE
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