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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 040126

Area Forecast Discussion
National Weather Service Honolulu HI
326 PM HST Sat Jun 3 2023

A ridge to the north will weaken and shift southward during the
next couple days in response to a pair of low pressure systems
passing by to the north. This will gradually ease the trade winds
and bring mostly dry weather to the islands through Tuesday.
Surface ridging will reestablish north of the island by midweek,
increasing trades back to moderate levels, with more typical
trade wind shower coverage.


Visible satellite imagery this afternoon is much the same as this
morning with high clouds continuing to stream west to east across
the state, thickest over Oahu, and scattered low clouds moving into
windward areas with a few very light embedded showers. Leeward
areas remain mostly dry. A cold front is still positioned around
700 miles northwest of Kauai and a weak surface ridge around 400
miles north of the state are keeping moderate trades in place. Sea
breezes have developed in the more sheltered leeward spots this
afternoon, with scattered inland clouds. A rather dry airmass will
persist into this evening, with only isolated showers expected.

The cold front to the north will push the ridge to the south, closer
to the islands over the next day or so, gradually weakening the
trades to more light to locally moderate speeds through Sunday.
The airmass is expected to moisten up a bit beginning tonight,
which should allow for a slight increase in windward showers.
Another surface trough is forecast to develop northwest of the
state Sunday night into Monday, further disrupting the ridge, then
stall north of Kauai Monday night. This will keep light to locally
moderate trades in place through early next week, with scattered
windward showers mainly overnight into early morning. With the
lighter background flow, nightly land breezes with mostly clear
skies over leeward areas will give way to afternoon sea breezes
and inland clouds and a few showers.

Weak upper-level troughing will persist near the state through
early next week, but is not expected to have much of an
enhancement effect on local shower activity due to the relatively
dry airmass still in place over the state. It will, however, keep
periods of high clouds over the islands with varying thicknesses
into the middle of next week, which could result in slightly
warmer overnight lows and cooler daytime highs, depending where
the thickest clouds set up. Have nudged low temperatures up a few
degrees for tonight, mainly for Oahu, as a result.

As the surface trough weakens and dissipates on Tuesday, surface
ridging from high pressure centers well northwest and northeast of
the state will build back in to our north. Trade wind speeds will
gradually increase to moderate to locally breezy levels through
the remainder of the week. Models are indicating a slight increase
in low-level moisture for the second half of the week, which would
result in more typical trade wind shower coverage for windward
areas with the occasional shower making it over to the leeward


Gentle to locally moderate trade winds for the rest of the
weekend while maintaining limited showers across windward areas.
VFR conditions expected through Sunday.

AIRMET Tango remains in effect for tempo moderate turbulence
statewide between FL250 and FL350 due to upper level jet dynamics
over the islands. The jet will linger around the state through
the weekend, maintaining high clouds over the area.


No change to the marine grids with the afternoon package, with the
forecast on track. Light to moderate trade winds are expected
into the start of the new week due to a disruption in the ridge to
the north of the islands. The ridge is expected to strengthen
again by midweek, bringing a return to moderate to locally fresh

Background long-period southerly swells will maintain small surf
along south facing through much of the new week. The first in
these swells started to arrive in the islands late this morning,
and was generated by a recent Tasman Sea source (south-southwest
direction), then continue into early next week. A mix of this
south-southwest swell and a fresh south-southeast medium period
swell from a system passing well south of Tahiti and the Tuamotus
at the end of May is expected from late Monday through midweek. As
these sources fade by Thursday, another small background south-
southwest swell is expected Friday into next weekend.

Surf along north facing shores will remain near the seasonal
average each day through the first half of next week. Although
the latest guidance continues to show a decent out of season
northwest swell arriving late next week, confidence remains low
at this point due to the source quickly lifting north-northeast
over the far northwest Pacific Sunday and Sunday night.

Surf along east facing shores will remain small through next week
due to the light trades locally and far upstream of the state over
the far eastern Pacific.





MARINE...M Ballard

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