Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Sat Mar 07 2020

Valid 00Z Sun Mar 08 2020 - 00Z Sun Mar 15 2020

Windy conditions are expected through the weekend as a strong area
of high pressure passes north of Hawaii. Embedded moisture will
allow mainly windward driven showers with possibility for some
lighter spillover into leeward areas given the stronger winds.
Trades should gradually relax some by early next week, and begin
veering to southeasterly as the high moves farther east. A number
of model solutions continue to show the potential for a cold front
to affect Hawaii by Wed night through the end of next week. A
northern stream shortwave is forecast to amplify well northwest of
Hawaii and separate from the northern stream in the form of a
cutoff upper-level low. Some previous runs of the GFS had
suggested the upper low might retrograde, but the latest runs have
backed off this idea, and models now show somewhat better
consensus that the upper low should drift east through late in the
week with a cold front affecting Hawaii. The ECMWF seems to be in
the middle of the spread in terms of timing, and would bring the
front into the western islands as soon as Wed night. Significant
question remains as to how much deep tropical moisture will be
pulled north into the system. The ECMWF has backed off a bit
compared to last night on the moisture advection, with both the
ECMWF and GFS now keeping the deepest moisture just south of
Hawaii. Nonetheless, expect continued model variability on that
aspect, with at least some possibility for heavy rains along/ahead
of the front next week. At this time, based on the current
deterministic and ensemble guidance, it appears the greatest
probabilities for heavier rains would be across the Big Island
late in the week into next weekend (when the front could
potentially stall). Forecast confidence by that time is relatively
low, however, given the uncertainty with respect to deep moisture
advection.

Ryan