Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
730 AM EST Thu Feb 01 2018

Valid 00Z Fri Feb 02 2018 - 00Z Fri Feb 09 2018

...Heavy rain threat for Kauai and Oahu through the weekend...

Very deep troughing to the west of Hawai'i near the Dateline
(500mb height anomalies around -4 standard deviations) will hold
in place until this weekend when it will move eastward. This will
drive a front through the region early in the week with
northwesterly upper flow behind it by Thursday.

The models and ensembles were in good agreement through about next
Tuesday/Wednesday with the approach of the front (early Monday in
the northwesternmost islands). Through the weekend, old surface
boundaries (moisture axes) to the northwest of the region will
maintain a moist southerly to southeasterly flow and the continued
risk of modest to locally heavier rain for Oahu/Kauai/Ni'ihau.
Precipitable water values will be in excess of 1.5 inches or +2 to
+3 standard deviations. The approaching cold front on Monday will
push the rain to the southeast through the rest of the region on
Tuesday and the to the east of the Big Island on Wednesday. By
then, the ensembles diverge in timing with the GEFS members
generally quicker with the upper trough than the ECMWF/Canadian
members. The deterministic runs were generally close in timing to
their ensemble members. Prefer a timing slower than the GEFS
members near the ECMWF ensemble mean, which was a bit weaker than
the deterministic 00Z ECMWF.


Fracasso