482
FXHW01 KWNH 110755
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
355 AM EDT WED MAR 11 2026
VALID 00Z THU 12 MAR 2026 - 00Z THU 19 MAR 2026
...PROLONGED AND POWERFUL KONA STORM TO BRING NUMEROUS IMPACTS
ACROSS HAWAII INTO EARLY NEXT WEEK...
A HIGH-IMPACT AND POTENTIALLY LIFE-THREATENING WEATHER PATTERN
WILL CONTINUE TO UNFOLD ACROSS HAWAII INTO EARLY NEXT WEEK. MODEL
GUIDANCE REMAINS IN GOOD AGREEMENT WITH THE EVOLUTION OF THE
POWERFUL KONA STORM CENTERED A LITTLE OVER 1,000 MILES NORTHWEST
OF THE ISLAND CHAIN. AT THE SURFACE, A BROAD CYCLONIC CIRCULATION
WITH CENTRAL PRESSURES AOB 990 MB WILL REMAIN POSITIONED TO THE
NORTHWEST, TIGHTENING THE PRESSURE GRADIENT ACROSS THE ISLANDS.
ALOFT, A POTENT, LARGE-SCALE TROUGH WILL SHARPEN AND TAKE ON A
DISTINCT NEGATIVE TILT AS A 120-140 KT JET STREAK ON ITS WESTERN
FLANK DIGS SOUTHEAST. THIS CONFIGURATION WILL FOSTER A PROLONGED
PERIOD OF SIGNIFICANT LARGE-SCALE UPPER-LEVEL DIVERGENCE AND THUS
DEEP-LAYER ASCENT, WHICH WILL MAINTAIN WIDESPREAD AREAS OF
ORGANIZED CONVECTION WITH EMBEDDED THUNDERSTORMS FOR SEVERAL DAYS.
TROPICAL MOISTURE (PWAT VALUES 1.75-2.00") WILL CONTINUE TO
EXPAND EASTWARD ACROSS THE ISLANDS WEDNESDAY AND THURSDAY, THEN
PEAK BETWEEN 2.00-2.25"+ BY FRIDAY AND SATURDAY DURING THE PERIOD
OF STRONGEST LEFT-EXIT REGION UPPER FORCING (DIVERGENCE ALOFT AND
ROBUST SOUTHERLY AGEOSTROPHIC BOOST TO THE LOW-LEVEL FLOW). BY THE
WEEKEND, THE CONCERN WILL BE WITH THE LIKELY ADDITIONAL HEAVY
RAINFALL OVERTOP ALREADY SATURATED SOILS, AND THEREFORE THE RISK
OF SIGNIFICANT FLASH FLOODING STATEWIDE. PER BOTH THE GFS AND
ECMWF, SATURDAY AND SUNDAY WILL BE THE DAYS WHEN THE INTEGRATED
WATER VAPOR TRANSPORT OR IVT VALUES ARE MOST ANOMALOUS -- PEAKING
AROUND OR ABOVE 1,000 KG/M-S. DURING THE SAME TIME, THE 00Z 03/11
GEFS SHOWS PWAT VALUES PEAKING BETWEEN 4 AND 5 STANDARD DEVIATIONS
ABOVE NORMAL, ALSO QUITE RARE FOR EARLY MARCH.
THE LATEST ECMWF ESAT OUTPUT CONTINUES TO UNDERSCORE THE EXTREME
NATURE OF THIS EVENT, WITH EXTREME FORECAST INDEX (EFI) VALUES FOR
BOTH QPF AND PWAT REACHING 0.99 TO 1.00, OR THE MAXIMUM POSSIBLE
ANOMALY. MOREOVER, THE 24-HR QPF RETURN PERIODS FOR SEVERAL ECMWF
ENSEMBLE MEMBERS OVER THE WEEKEND, WHEN AVERAGE 24HR RAINFALL
PEAKS BETWEEN 3-6+ INCHES, SUGGEST A 25 TO 50 YEAR AVERAGE
RECURRENCE INTERVAL OR ARI (2-4% ANNUAL EXCEEDANCE PROBABILITY OR
AEP). SHIFT-OF-TAILS OR SOT VALUES OF 1 TO 2 ARE NOTED ACROSS MOST
ISLANDS, WITH LOCALIZED POCKETS EXCEEDING 2.0 ON THE WINDWARD
SLOPES OF THE BIG ISLAND AND THE TERRAIN OF MAUI. VALUES ABOVE 1.0
SUGGEST AN EXTREME TO POTENTIALLY RECORD-BREAKING RAINFALL EVENT
FOR THIS TIME OF YEAR, WHICH PROVIDES HIGH CONFIDENCE IN THE
POTENTIAL FOR CONSIDERABLE FLASH FLOODING.
HURLEY
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