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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 270627
Area Forecast Discussion
National Weather Service Honolulu HI
827 PM HST Mon Sep 26 2022
Trade winds will strengthen to light to moderate this week which
will focus low clouds and showers across mainly windward areas.
Winds may be light enough at times to allow localized afternoon
sea breezes to generate clouds and a few showers across leeward
Radar this evening shows only scattered to isolated showers
across the islands, with a majority of showers lingering west of
the state in an area of deeper moisture. Otherwise, satellite
data shows limited cloud cover this evening, as drier air
continues to stream in from the east. Overall expect limited
clouds and showers to influence the islands through early Tuesday,
as dry and stable air moves westward.
A surface boundary about 400 miles north-northeast of the islands
will further weaken as it slowly drops southward toward the state
into Wednesday, while the surface ridge north of the state
gradually reestablishes itself. This pattern will maintain a weak
pressure gradient and light to moderate easterly trade wind flow
across the islands this week. These winds will direct showers to
mainly windward areas in a typical trade wind weather pattern.
However, localized sea breeze clouds and showers remain possible
for some leeward areas this week.
The airmass will differ across the state this week, as the front
sagging southward maintains a layer of deeper moisture over the
western islands, while much drier and more stable air continues to
filter in across the central and eastern islands through much of
this week. Forecast moisture depths and inversion heights will
remain around 7k feet across the eastern half of the state with
PW values generally around 1.25 inches or less. Deeper moisture
depths between 8k-10k feet and PW values over 1.60 inches or
greater, are forecast over the western end of the state. This
pattern will limit the areal coverage of showers for Maui and the
Big Island into Friday, while the areal coverage of showers
increasing across Oahu and Kauai.
Current trends support a weaker pressure gradient redevelops once
again this weekend, as another surface boundary drops southward.
The weakened surface pressure gradient could allow for localized
afternoon and early evening sea breeze showers across some leeward
areas and island interiors this weekend.
A ridge of high pressure passes north of Hawaii this evening
producing gentle to moderate trade winds. Trade winds will
strengthen slightly to more predominantly moderate levels on
Tuesday. Few to scattered clouds around the islands will decrease
in coverage overnight with benign weather expected on Tuesday. VFR
conditions will prevail over the next 24 hours and no AIRMETs are
A front will remain in place between a high to our north and the
main Hawaiian islands. This will keep trade winds in the light to
moderate range over the next several days for most waters.
However, terrain-induced acceleration may briefly boost winds to
Small Craft Advisory threshold Tuesday and Tuesday night across
typically windy waters around Maui and the Big Island.
South swell will continue to lower through Wednesday. Another
small longer period south swell will fill in Wednesday night and
Thursday with a slight reinforcement expected Friday and Saturday.
A slightly larger long period south swell may arrive around
Sunday. No significant north or northwest swells are expected
through Thursday night, with a small short period northwest swell
expected Friday and Saturday. Another small but longer period
northwest swell may arrive on Sunday. Short period choppy surf
will remain rather small over the next few days across east-facing
shores, with a slight increase possible later in the week and on
into the weekend.
Small Craft Advisory from 6 AM Tuesday to 6 AM HST Wednesday 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