Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
820 AM EDT Thu Oct 25 2018

Valid 00Z Fri Oct 26 2018 - 00Z Fri Nov 02 2018

...Heavy rain threat for Hawai'i next week...

Longwave pattern across the Pacific remains much the same from
yesterday with a significant upper trough and surface cold front
developing/deepening just west of the region early next week. This
will support an increasingly wet pattern for first the western
island and then eastward. Additionally, some models spin off a
coherent surface low off the ITCZ and bring it northeastward over
the western islands next week which may act to enhance an already
wet pattern. Predictability is low in such a solution but all the
latest deterministic models show a sfc low tracking across
Kauai/Oahu. Trades will veer from ENE to E to SE and eventually
south as the trough and surface cold front approach next week.

Heavy rainfall threat potential is high with this pattern given
the amplitude of the trough (500mb heights about 3 standard
deviations below average) and surge of tropical moisture from the
ITCZ (probability of precipitable water values greater than 2
standard deviations above average > 70% per the GEFS). Several
inches of rain are possible over especially the western islands
and southwestward/southward-facing terrain but the entire state
has the potential for significant rain next week as mesoscale
processes/convection will also play a role in focusing rainfall.


Fracasso