973
FXHW01 KWNH 260928
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
528 AM EDT MON OCT 26 2026
VALID 00Z TUE 27 OCT 2026 - 00Z TUE 03 NOV 2026
IMPACTFUL WEATHER IS EXPECTED TO IMPACT PORTIONS OF THE STATE BY
TUESDAY INTO WEDNESDAY WITH AREAS OF HEAVY RAINFALL AND FLASH
FLOODING. A WEAK WAVE OF LOW PRESSURE ALONG AN ELONGATED TROUGH
AXIS SHOULD MOVE ACROSS THE STATE DURING THIS TIMEFRAME, BRINGING
AN INCREASE IN FORCING AND SOUTHWESTERLY LOW LEVEL WINDS AND
MOISTURE TRANSPORT. MODELS CONTINUE TO CONVERGE ON THE TIMING OF
THIS FEATURE, WITH TUESDAY AFTERNOON INTO WEDNESDAY NIGHT
APPEARING MOST LIKELY AT THIS TIME.
THERE ARE SEVERAL FAVORABLE INGREDIENTS FOR HEAVY RAINFALL WITH
THIS SYSTEM. SYNOPTIC FORCING WILL BE STRONG WITH FAVORABLE RIGHT
ENTRANCE REGION UPPER JET DYNAMICS. PWS WILL BE IMPRESSIVELY HIGH,
WITH VALUES INCREASING TOWARDS 2.5". INSTABILITY IS NOT FORECAST
TO BE OVERLY ROBUST, BUT GIVEN THE IMPRESSIVE DYNAMICS AND STRONG
LOW LEVEL CONVERGENCE, EVEN WEAK INSTABILITY SHOULD BE ENOUGH FOR
THUNDERSTORM DEVELOPMENT DURING THE PEAK OF THE EVENT SOME POINT
BETWEEN LATER TUESDAY AND WEDNESDAY NIGHT. SOME LATITUDINAL
ADJUSTMENT OF THE MAX RAINFALL AXIS IS POSSIBLE, BUT AT THE MOMENT
THE BEST MODEL CLUSTERING SUPPORTS OAHU TO MAUI HAVING THE MOST
CONCENTRATED CONVECTIVE THREAT. SOME FLASH FLOOD THREAT APPEARS
LIKELY, AND SIGNIFICANT IMPACTS ARE A POSSIBILITY.
BY THURSDAY INTO THE WEEKEND THE MAGNITUDE OF FORCING SHOULD
DECLINE, BUT THE TROUGH AXIS WILL REMAIN NEARBY AND PWS WILL
STAY ELEVATED. THUS WHILE THE COVERAGE OF HEAVIER RAINFALL SHOULD
DECREASE, THE THREAT FOR LOCALLY HEAVY RAINFALL AND SOME FLASH
FLOODING WILL PERSIST. MORE UNCERTAINTY ON THE DETAILS BY THIS
TIME, BUT IT LOOKS MORE LIKELY THAT THE HEAVIEST RAINFALL WILL
FOCUS ACROSS THE NORMALLY FAVORED WINDWARD AREAS OF MAUI AND THE
BIG ISLAND.
CHENARD
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