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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 200657

Area Forecast Discussion
National Weather Service Honolulu HI
857 PM HST Sun May 19 2024

The low pressure system far north of the state will continue to
drift slowly northward over the next few days. The high pressure
ridge will build in north of the state as the low drifts away from
the island chain. Expect moderate to locally breezy east to east-
southeast winds over most islands through Wednesday, wind directions
will be modified by local scale daytime sea breezes over terrain
sheltered areas of each island. Brief passing showers will mainly
drift over windward and mountain areas in the evening through
early morning hours.


Satellite imagery this evening shows a band of middle and high
clouds drifting over the eastern end of the Hawaiian Islands.
Upper air balloon soundings from 2 PM HST at Lihue and Hilo show
subsidence temperature inversion heights in the 5,000 to 6,000
foot elevation range. These low temperature inversion heights
indicates a stable air mass with strong subsidence across the
state and are expected to continue into Tuesday for most islands.

Tuesday through Wednesday...A low level easterly wave, shown on
satellite imagery east of the Big Island around 147W longitude and
the GFS 700 MB streamlines, will move into the eastern islands of
Maui and the Big Island late Tuesday. This trough will increase
inversion heights and allow deeper clouds and higher shower trends
to develop over the eastern slopes of both islands. By Wednesday
this trough moves into the central islands spreading increasing
cloud and shower trends to windward and mountain areas statewide.

Thursday through Saturday...Moderate to locally breezy trade winds
remain in the forecast with broad upper level troughing will keep
passing showers mainly during the overnight to early morning hours
favoring windward and mountain areas.


Light to moderate east to southeast winds will persist through
the 24-Hr forecast period and beyond. Although VFR conditions
will prevail, brief periods with MVFR CIGs/VSBYs in showers moving
through are possible over windward areas overnight into Monday
morning. Afternoon showers are also possible over leeward areas
where localized sea breezes form.

AIRMET TANGO remains in effect for moderate upper level
turbulence from FL250-350, which will likely continue into

AIRMET Zulu is in effect for areas of light to moderate rime
icing in the layered clouds from Maui to the Big Island.
Conditions should gradually improve from west to east overnight as
the mid to high clouds drift eastward.


Maritime moderate easterlies, with localized fresh to strong winds
through eastern island bays, channels and south of Big Island,
will persist through the week. A Small Craft Advisory (SCA) is
currently in effect through Monday afternoon for the notoriously
windier waters surrounding Maui County and Big Island. Winds
through Maalaea Bay and Pailolo Channel may reach SCA thresholds
by Monday night. Therefore, the SCA may need to be expanded in
areal coverage to include these zones.

Surf along south-facing shores will remain at or near advisory
heights tonight. Evening south shore buoy observations of 3 to 4
foot, near 16 second swell, with spectral density plots showing
additional long period energy reaching southern shores this
evening, will likely maintain High Surf Advisory (HSA) surf into
the early Monday morning hours. This warrants a continuance of the
HSA for south-facing shores through Monday sunrise. The HSA may
need to be extended through the morning but will be likely be
dropped by Monday afternoon. As the south swell fades, south shore
surf is forecast to wane from Monday through the middle of the
week. The current very small northwest swell will gradually ease
through Monday with resultant north shore surf conditions falling
to near flat from Tuesday on through next weekend. East chop will
remain steady through early week. There may be a slight mid to
late week uptick in wind waves as trades strengthen a bit upstream
of the islands.


High Surf Advisory until 6 AM HST Monday for south facing shores
of all islands.

Small Craft Advisory until 6 PM HST Monday for Maui County
Windward Waters-Alenuihaha Channel-Big Island Windward Waters- Big
Island Leeward Waters-Big Island Southeast Waters.

Wind Advisory until 6 AM HST Monday for Big Island Summits.




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