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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 231942

Area Forecast Discussion
National Weather Service Honolulu HI
942 AM HST Sat Sep 23 2023

High pressure far northwest of the islands will keep moderate to
breezy trade winds in place through late next week, with only
minor fluctuations in strength. Fairly typical trade wind weather
will prevail, with showers favoring windward and mauka areas and a
stray shower reaching leeward communities at times.


A 1028 mb surface high is located far northwest of Hawaii this
morning blowing moderate to breezy trade winds across the state.
Visible satellite showers scattered low clouds anchored along the
windward slopes with a bit more clouds and showers across windward
Big Island. Expect decreasing shower coverage this afternoon
followed by a boost later tonight. Shower coverage will generally
be slightly less Sunday through Tuesday. With the trades blowing,
low clouds and showers will favor windward and mauka areas
through the next week, mainly at night and during the early
morning hours, with a few showers reaching leeward areas at times.

Trade winds speeds will weaken slightly around Monday as a front
to the north of the islands moves closer and then weakens. High
pressure filling in behind this feature will again boost winds
speeds back to current levels from Tuesday onward.


Locally breezy easterly trade winds will continue to prevail
across the island chain through the weekend as high pressure
remains anchored to the far northwest of the islands. Showers and
occasional low clouds will favor north through east sections of
the islands throughout the forecast period, especially during the
overnight through morning hours each day. VFR conditions will
prevail at most locations, but isolated MVFR ceilings and
visibilities cannot be ruled out within any showers that move

MVFR conditions along windward sections of Maui and the Big
Island that prevailed earlier this morning have begun to
diminish. Therefore, AIRMET Sierra for mountain obscuration across
these areas has been cancelled.

AIRMET Tango for moderate low level turbulence remains in effect
downwind of the terrain of all islands this morning. This AIRMET
will likely be needed through at least early evening.


A broad area of surface high pressure located far north of the
state will continue to produce locally strong trade winds this
weekend. As a result, the Small Craft Advisory (SCA) has been
extended through Sunday afternoon for the typically windier
waters adjacent to the islands of Maui County and the Big Island.
The latest forecast indicates the trade winds may remain locally
strong from Sunday night through early next week. Therefore, the
SCA may eventually need to be extended for the same typically
windier waters in the vicinity of the eastern islands during
Monday / Tuesday. Note that SCA conditions may develop over
additional waters by the middle of next week if the gusty trade
winds become more widespread.

The current small, medium-period southwest (210 degrees) swell
will continue to gradually lower today. A new small, long-period
southwest (210 degree) swell is expected to arrive by Sunday.
This southwest swell energy combined with a lingering southeast
trade wind swell will likely maintain small surf along south
facing shores through early next week.

A small, medium-period north-northwest (330 degrees) swell
started to fill in overnight and will continue to spread down the
island chain today. This small bump should peak on Sunday and will
likely cause a slight bump in surf along exposed north and west
facing shores this weekend. In addition, a small north (350-360
degrees) swell may arrive around Tuesday, followed by a modest
north-northeast (020 degrees) swell from Thursday into Friday.

Moderate, rough surf will likely persist along east facing shores
into early Sunday. The surf may lower slightly along east facing
shores from late Sunday into Tuesday due to a slight weakening of
the trade winds. Moderate, rough surf may return along east facing
shores by the middle of next week due to strengthening of the
trade winds.


Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.




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