Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
730 AM EST Mon Feb 04 2019

Valid 00Z Tue Feb 05 2019 - 00Z Tue Feb 12 2019

A transient mid/upper-level ridge builds across Hawaii today as a
broad 500 hPa weakness which has been across Hawaii for several
days moves east. This allows drier air to filter across the state
bringing a reduction in shower activity and a resumption of 10-20
kt surface easterlies. Models still show significant flow
amplification developing over the north/central Pacific by
mid-week as shortwave energy separates from digging northern
stream flow and continues to amplify north of Hawaii. Showers
should increase across Hawaii as moisture advects north into
developing low pressure in disrupted trade flow.

Guidance generally agrees that late week mid-upper level trough
reinforcement will act to further dig height falls into the state,
but differences remain with flow evolution details. The latest
UMMET/Canadian/NAVGEM develop quite the closed low just to the
north of the state by Saturday while the GFS/ECMWF offer a slower
scenario with several shortwave troughs that do not
consolidate/close until Sun/Mon. Given the range of possible
scenarios, recommend an ensemble mean approach, as ensemble means
show a bit more consistency. Ensembles are closest to the ECMWF.

Given the degree of amplification expected, there seems to be
consensus that a cold front may push through Hawaii by Fri,
bringing drier air across Hawaii and a period of brisk
northwesterly flow at the surface. Uncertain height falls but
likley closed low development and proximity could act support
renewed showers this weekend.

Schichtel