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