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Hawaiian Islands Synoptic Discussion and Guidance

934
FXHW60 PHFO 242005
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1005 AM HST Fri Sep 24 2021

.SYNOPSIS...
Locally breezy trade winds will bring passing clouds and showers to
mainly windward and mountain areas through the weekend and into next
week. A weak surface trough passing south of the islands will boost
rainfall across windward Big Island late Saturday and Sunday.

&&

.DISCUSSION...
A surface ridge to the N of the islands will maintain trade winds
through the weekend and into next week, with locally breezy
conditions prevailing. The island atmosphere will remain stable, but
this will not prevent the trade winds from occasionally delivering
showery low clouds that will dampen primarily windward and mauka
areas from time to time. One such cloud cluster is moving in on
Kauai, with another cluster a little ways E of windward Big Island
and Maui that will likely arrive by this evening.

A more significant area of moisture, associated with a surface
trough, is about 900 miles SE of the Big Island. Model guidance
continues to indicate this trough and associated moisture moving
toward the islands over the next 2 days, with the trough passing S
of the islands Saturday night and Sunday, potentially leading to an
increase in showers over the Big Island (and maybe windward Maui).
Otherwise, guidance is not indicating any organized moisture sources
into next week. Trade winds will likely receive a boost in strength
as the trough passes as well.

&&

.AVIATION...
Clouds and showers associated with a weak trough embedded within
locally breezy trades reached Oahu during the predawn hours
prompting issuance of AIRMET Sierra for mountain obscuration.
Conditions have begun to improve and this AIRMET is expected to
expire as scheduled around noon HST. Trades will undergo modest
strengthening and clouds and showers will increase in coverage
over windward and mauka areas this evening through the first half
of tonight as aforementioned trough axis advances through the
island chain. AIRMET Sierra may be needed for portions of the
island chain during this time.

AIRMET Tango for lee turbulence has been issued and will remain
in effect through at least tonight and possibly through Saturday.

&&

.MARINE...
A ridge of high pressure far north of the state will generally
maintain moderate to locally strong trades through early next week.
A surface trough is expected to move into the southeast offshore
waters Saturday and pass south of the Big Island Saturday night.
As this trough passes south of the state, the pressure gradient will
tighten and will result in a slight increase in wind speeds Saturday
night through Sunday. Widespread fresh to strong winds are expected
during this time and we could see the Small Craft Advisory (SCA)
expanded into other areas. Currently our SCA is only in effect for
the windier waters around Maui County and the Big Island.

Buoy observations indicate the new long-period north- northwest
swell is larger than initially expected and will bring high surf to
exposed north and west facing shores. The swell is likely near its
peak around Kauai this morning and should continue to build across
the rest of the island chain through this afternoon. A High Surf
Advisory is in effect for north and west facing shores of Kauai and
north facing shores of Oahu, Molokai and Maui. For north facing
shores next week, small surf is expected with only small swells from
the north and north-northwest. No significant swells are expected
along south and east facing shores.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Saturday for north and west facing
shores of Kauai and Niihau and for north facing shores of Oahu
Molokai and Maui.

Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

Small Craft Advisory until 6 AM HST Saturday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-Oahu
Windward Waters-Kaiwi Channel-Maui County Windward Waters.

&&

$$

DISCUSSION...Birchard
AVIATION...JVC
MARINE...Kino

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



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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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