Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EST Sat Jan 28 2023

Valid 00Z Sun Jan 29 2023 - 00Z Sun Feb 05 2023

A rather wet weekend and early next week are in store for much of
Hawaii. A surface trough currently causing heavy rainfall and
flooding across Maui will remain across the islands and gradually
drift west over the next couple days, helping to focus moisture
and showers. Model guidance such as the HREF indicates that the
main axis of showers could drift atop Molokai and perhaps as far
west as Oahu Saturday into Sunday, and the Honolulu Forecast
Office has a Flash Flood Watch in place from Oahu to Maui for the
potential of continued training showers. Meanwhile aloft, a closed
low is in place centered around 40N, and its trough is expected to
lengthen, with upper-level energy drifting southward over the
state and closing off a subtropical upper low by around 12Z Monday
perhaps centered just to the southwest of Hawaii. This will draw
in deep tropical moisture as well as provide instability with a
removed inversion given the lowering heights aloft, for even more
support for widespread rain and thunderstorms. Moisture levels
will be quite high with precipitable water values showing to be
over the 90th or 95th percentiles. Recent ECMWF runs hit the Big
Island particularly hard with heavy precipitation around Monday,
while GFS runs show the heaviest totals offshore, but the
potential is certainly there for heavy amounts across much of the
state. More instances of flooding are certainly possible. Kauai
may see a wetter trend by Sunday and especially Monday, but
regardless will start out on the backside of the upper trough/low
and could see continued breezy north-northeasterly winds through
early next week. Models generally indicate that the closed upper
low should drift a bit west away from the state around
Tuesday-Wednesday but be slow to erode. This would allow for some
above average moisture to be present even through midweek and
beyond, but likely to a lesser extent. Meanwhile more typical
trade winds are forecast to set up at the surface, so a wet trade
wind pattern looks to be in store through the latter part of next
week.

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