077
FXHW01 KWNH 070715
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
315 AM EDT TUE APR 7 2026
VALID 00Z WED 08 APR 2026 - 00Z WED 15 APR 2026
...MULTI-DAY HEAVY RAIN THREAT AS DEEP TROPICAL MOISTURE AND UPPER
LOW IMPACT THE ISLANDS...
A SIGNIFICANT PATTERN CHANGE IS UNDERWAY AS A LEADING SHORTWAVE
TROUGH AND ASSOCIATED COLD FRONT APPROACH THE STATE FROM THE WEST.
WHILE THE FRONT ITSELF IS FORECAST TO REMAIN WEST OF THE
ISLANDS, LOW-LEVEL WINDS WILL VEER TO THE SOUTH AHEAD OF THE
BOUNDARY, DRAWING A PLUME OF TROPICAL MOISTURE NORTHWARD ACROSS
THE CHAIN BEGINNING TUESDAY. THIS MOISTURE SURGE WILL BEGIN TO
ELEVATE THE POTENTIAL FOR WIDESPREAD HEAVY RAINFALL. MEANWHILE, THE
INITIAL SHORTWAVE WILL WEAKEN AND LIFT NORTHEAST, GIVING WAY TO A
MORE AMPLIFIED SHORTWAVE DIGGING SOUTHEASTWARD. GUIDANCE REMAINS
IN GOOD AGREEMENT THAT A CLOSED UPPER-LEVEL LOW WILL DEVELOP WELL
NORTHWEST OF THE STATE BY WEDNESDAY, DRIFTING SLOWLY EASTWARD
THROUGH THURSDAY. AS SURFACE LOW PRESSURE ORGANIZES ALONG THE
STALLED BOUNDARY, AN ADDITIONAL SURGE OF DEEP MOISTURE IS EXPECTED
TO OVERSPREAD THE ISLANDS.
MODEL ENSEMBLES, INCLUDING THE GEFS, ECENS, AND CANADIAN, CONTINUE
TO INDICATE THAT ORGANIZED HEAVY RAINFALL IS LIKELY BY THURSDAY
INTO FRIDAY, WITH THE HIGHEST THREAT FOCUSED INITIALLY OVER THE
WESTERN ISLANDS AS THE UPPER LOW CONTINUES ITS SLOW APPROACH.
WHILE PROBABILITIES FOR 24-HOUR QPF EXCEEDING ONE INCH BEGIN TO
DIMINISH AND SHIFT TOWARD THE CENTRAL AND EASTERN ISLANDS FRIDAY
INTO SATURDAY, THE THREAT FOR FLASH FLOODING REMAINS ELEVATED. BY
FRIDAY, THE UPPER LOW SHOULD BEGIN LIFTING OUT TO THE NORTHEAST AS
IT INTERACTS WITH ANOTHER LOW TO ITS NORTH. HOWEVER,
SOUTHWESTERLY FLOW ALOFT WILL PERSIST OVER THE ISLANDS THROUGH
EARLY NEXT WEEK, MAINTAINING ABOVE-NORMAL PRECIPITABLE WATER
VALUES. THIS TROPICAL AIRMASS, COMBINED WITH A LINGERING SURFACE
BOUNDARY, MAY SUPPORT CONTINUED PERIODS OF HEAVY RAIN AND
LOCALIZED FLASH FLOODING THROUGH THE END OF THE PERIOD.
PEREIRA
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