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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 181929

Area Forecast Discussion
National Weather Service Honolulu HI
929 AM HST Tue Jun 18 2024

Ongoing breezy and dry trades will turn locally strong and become
somewhat wetter Thursday into the weekend.



The sharp trade wind inversion around 5kft on this morning's
soundings highlights the stable pattern in place over the forecast
area. This is in spite of an upper low positioned directly overhead,
which is doing little more than producing periodic patchy high
clouds, a testament to existing strong mid-level stability. Low-
level water vapor imagery shows an even drier appearance to the
upstream airmass suggesting stability will further strengthen during
the next 24-48 hours. During this time, breezy trades will continue
delivering shallow and mostly light shower activity windward and
mauka as has been the case for the last couple of days.

Meanwhile, troughing along the US West Coast is seeding the upstream
trade wind environment with increased moisture that is poised to
arrive during the latter half of the week. Model consensus remains
in tact that trades will become locally strong while also acquiring
a wetter character Thursday night into the weekend. Showers will
occasionally drift into the typically drier leeward zones, mainly
overnight and during the early morning, as deeper moisture forces
the inversion to lift and weaken.



Breezy trades will continue, with SHRA and low cigs favoring
windward and mauka locations. Periods of MVFR conds are possible
in any SHRA. Otherwise, VFR conds should prevail. Trade winds are
expected to slightly strengthen to locally strong speeds during
the next 24 hours.

AIRMET Sierra is in effect for mtn obsc for windward portions of
Maui, Molokai, Oahu and Kauai. AIRMET TANGO is also now in effect
for low level turbulence lee side of mountains due to the trade
winds strengthening during the next 24 hours.



Fresh to strong trade winds will persist for the next couple of
days as a 1025 mb surface high strengthens and drifts around 650
to 800 nm northeast of the state. A Small Craft Advisory (SCA) is
in effect for most waters around the Big Island and Maui. As the
high settles far north of the islands Thursday and Friday, trade
winds will increase a notch, bringing near gale conditions and
elevated seas in some channels. The SCA will likely be expanded
to most waters at that time and continue through the weekend.

The current south swell will fade out over the next 24 hours,
followed by a lull in south shore surf into Friday. A mix of
small, long-period south swell and a shorter period southeast
swell may push shores up near seasonal average during the
weekend. As this swell slowly declines early next week, another
long-period south-southwest swell will fill in.

Surf along east-facing shores will gradually trend up through the
weekend. The trade wind swell is currently near seasonal average
at about 6-7 feet at 7 to 8 seconds. Expect a slight increase
Thursday and Friday, followed by an increase above seasonal
average this weekend.

Surf along north-facing shores will return to seasonally tiny
levels later today as a small northwest swell fades. No
significant swells are seen in the short term, through a very
small pulse is possible early next week.


Small Craft Advisory until 6 PM HST Thursday for Kaiwi Channel-
Maui County Windward Waters-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