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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 310634

Area Forecast Discussion
National Weather Service Honolulu HI
834 PM HST Sat May 30 2020

Expect trade wind weather through the entire forecast period as
high pressure remains north of the area. Clouds and showers will
favor windward and mauka areas, with generally dry weather
expected over most leeward locations. An old frontal boundary
interacting with island terrain may produce increased showers
Tuesday and Wednesday.


A surface high northwest of the main Hawaiian Islands is driving
moderate trade winds across local waters this evening. This high
will remain nearly stationary through Sunday night, then move to
a position northeast of the area late Monday through Wednesday.
This will slightly decrease trade wind speeds. High pressure will
then rebuild due north of the area Thursday through Saturday,
prompting a trade wind speed increase.

Our airmass is rather dry and stable, with an upper ridge
centered several hundred miles to our north. Pockets of moisture
embedded within trade flow will fuel light passing showers over
windward and mauka areas, with most leeward locations remaining
generally dry. Moisture associated with the remnants of an old
front is forecast to move through the area Tuesday and Wednesday,
likely increasing shower coverage across windward and mauka areas.


A 1022 mb surface high located some 500 nm NW of Kauai will be
moving NE at 20 kt during the next 24 hours. In doing so, a
moderate NE trade wind flow will continue through Sunday. AIRMET
Tango could be needed after 311600z, as models are indicating a
slight boost in the trades.

Clouds and showers will be rolling in with the trade wind, causing
brief MVFR conditions to especially the windward and mountain
areas. The potential area for AIRMET Sierra early on is windward
Big Island, as abundant low clouds lies just off the coast. After
09z, a band of low clouds may impact the windward and mountain
areas of Maui, Molokai, and Oahu, that may bring on AIRMET Sierra.
On the other hand, a patch of low clouds with embedded showers will
be clearing Kauai by 08z. A shower or two may pop up along the
Kona coast as the evening progresses. Tops of the trade showers
are between 7 and 9k feet.


A high to the north of the area will maintain moderate to locally
breezy trade winds through the weekend, with winds possibly
approaching Small Craft Advisory (SCA) criteria in the windier
areas around Maui and the Big Island Sunday. The trades will
weaken Monday as the high moves northeast, but will rebuild
Wednesday into Thursday as the high strengthens.

South shore surf will be somewhat elevated this weekend, with a
larger south swell expected to gradually build from Monday into
Wednesday, then gradually diminish into Friday. Peak surf heights
could be large enough to warrant a High Surf Advisory (HSA) for
south facing shores of all islands, potentially as early as
Tuesday, but more likely Wednesday. Surf will remain well below
HSA levels along other shores through the period, although a
couple of small swells from the north and northwest will keep
surf from going flat along north facing shores. The latest Surf
Discussion (SRDHFO) contains details on the swell sources.






Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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