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Temp8.2 C
RH30 %
WindW 1 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 250158

Area Forecast Discussion
National Weather Service Honolulu HI
358 PM HST Sat Sep 24 2022

Light southeast flow and sea breezes will enhance showers across
island interiors this weekend. A ridge of high pressure
reestablishing north of the islands next week, will promote the
gradual transition from light trades early, toward a moderate to
locally breezy trade wind pattern through next weekend. The
strengthening trade wind pattern will redirect showers toward
windward areas next week.


A persistent pattern will remain anchored over the region this
weekend, with an area of high pressure well northeast of the state
and a weakening surface low lingering northwest near Midway. This
pattern will maintain a weak pressure gradient southeast flow
across the islands, allowing for the continued development of
afternoon and early evening sea breeze showers across leeward
areas and island interiors into the beginning of next week.

Current radar trends show showers developing across the islands
this afternoon and expanding in areal coverage across leeward
zones. As expected, plume development has once again organized,
especially the Molokai and Lanai plumes, as winds remain generally
light southeast. Rainfall intensity has begun to pick up some
late this afternoon, which combined with the showers slow
movement and training pattern, and CIMSS based data showing total
precipitable water estimates around 1.55 inches streaming in from
the east, keeps heavier showers a possibility into this evening.

The airmass across the state is forecast to remain basically
unchanged through the remainder of the weekend (precipitable water
values ranging between 1.40 to 1.60inch). Therefore expect the
areal coverage of showers will expand across the islands
Sunday in a similar pattern as today. However, the depth of
moisture forecast for Sunday is slightly lower compared to
today, which may tend to limit rainfall rates somewhat to end
the weekend.

Next week begins the transition toward strengthening trades.
A weakening surface boundary well north of the state will drop
southward toward the islands, maintaining lighter southeast
background flow, while increasing moisture and enhancing rainfall
chances over the westerns islands into Wednesday. These lighter
winds, will keep afternoon sea breeze showers a possibility for
leeward locations into early next week. The ridge north of the
state begins to reestablish itself by midweek, with easterly
trades increasing to moderate before further strengthening to
locally breezy by the weekend. Models still differ some with
respect to the exact timing of when trades finally strengthen
across the islands. The trade wind pattern developing mid week
will diminish chances for afternoon sea breeze showers leeward,
and once again redirect showers to mainly windward areas in a
typical trade wind weather pattern. Drying airmass streaming into
the region from the east through next week, will eventually
decease the areal coverage of windward showers, as precipitable
water values drop to around 1.25inches or less.


Sea breezes have brought in increasing clouds and a few showers
over island interiors this afternoon that will linger until
sunset. Brief mountain obscurations will occur with these showers.
Have added AIRMET Sierra for mountain obscuration for windward
portions of the Big Island over the next few hours as cloud build
ups have been a bit more extensive there, otherwise VFR conditions
will prevail elsewhere. This AIRMET will likely be cancelled
around or just after sunset. Land breezes will set in a keep cloud
cover and showers offshore. Expect a similar weather setup for
Sunday with building clouds and showers through the day.


A low far northwest of the main Hawaiian Islands will continue to
weaken the ridge just north of the state. Expect light to
moderate east to southeast winds through tomorrow. Models show a
front will stall north of the region by Tuesday, keeping light to
moderate winds in the forecast through the first half of next
week. Wind speeds may approach Small Craft Advisory thresholds by
the end of next week.

South swell will remain elevated through tomorrow, then decrease
tomorrow night, leaving only background south swell through the
first half of next week. A small north-northwest swell will keep
north shore surf elevated today before fading on Monday. Another
small north- northwest swell is forecast to arrive Tuesday and
Wednesday. West facing shores will see a small increase in surf
from the south swell and, to a lesser extent, the north-northwest
swell. Light trade winds will keep small surf in the forecast
along east facing shores through at least next Wednesday.






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