Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
346 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, this is the same time that integrated water vapor transport
values peak aoa 1,000 kg/m-s, which is highly anomalous for early
March (PWAT anomalies between 4 and 5 standard deviations above 
normal both Saturday and Sunday per the 00Z 3/11 GEFS). 

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