Image Department Meteorology
Meteorology_Home Weather_Server News/Seminars
Academics Application Contact_Us

Links Disclaimer

Menu of Text Products for the Hawaiian Islands and the Tropical Pacific/Atlantic Oceans:
Narrow the Menu List
Select Time Limit: 12 hours | 24 hours | 48 hours | 72 hours | No time limit
Select Product Type: All | Routine Bulletins/FCSTS | Warnings/Watches/Advisories | HAWN Weather | Tropical | Marine | Aviation | Daily Obs | Special
Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 260144

Area Forecast Discussion
National Weather Service Honolulu HI
344 PM HST Sat Sep 25 2021


Breezy trades will focus clouds and showers over windward and
mauka areas through the forecast period. A greater coverage of
showers, a few locally heavy, is forecast over Windward Big Island
tonight into Sunday as a trough approaches from the east. Drier
trade wind weather will prevail from Monday onward.



A trough southeast of the islands has caused mid-level flow to
veer to southeasterly across the forecast area. This has driven
the batch of stratocu presently over the nearshore waters
northwestward, or mostly parallel to the islands, preventing it
from fully coming onshore. Breezy easterly trades have nonetheless
supported some degree of windward and mauka showers while the
southeasterly flow at the top of the boundary layer has supported
fairly widespread cloud cover over Maui, Molokai, and Oahu.
Overnight, this corridor of veered flow in the lowest 10kft or so
will steer a trough supporting shower-bearing stratocu toward the
Big Island. The lead edge of this area of interest is located
about 200 miles southeast of Hilo at press time and is
demonstrating a reasonably healthy appearance on satellite, its
weak open circulation serving as evidence of modest organization.
Cloud tops in this area topped out around 10-15kft during the
favorable nocturnal period last night, and a similar presentation
is anticipated again tonight as it approaches the Big Island by
around midnight HST. Diminishing stability through the lowest
several thousand feet will lead to a high coverage of moderate
trade wind showers focused over Windward Big Island and, to a
lesser extent, Windward Maui. A few locally heavy showers will be
possible but their expected coverage and duration are expected to
fall short of causing flooding concerns. Trades will receive a
brief boost as the trough passes by to the south, especially in
the vicinity of the Big Island, but will otherwise remain in the
moderate to breezy category for the remainder of the forecast
period. Drier trade wind weather will resume as the moisture axis
shifts west of the islands on Sunday night.



Mid-afternoon satellite and radar imagery depict limited clouds
and showers that have have favored north through east facing
sections of the islands today within a breezy easterly trade wind
regime. VFR conditions have prevailed across the state today, and
should continue to prevail throughout the forecast period across
the smaller islands. Meanwhile, southeasterly flow aloft is
expected to help steer a surface trough that is currently located
south of the Big Island closer to the state tonight and tomorrow
morning. This round of enhanced moisture is expected result in
heavier and more widespread showers, reduced visibilities, lower
ceilings, and mountain obscuration for windward portions of the
island. Elsewhere, MVFR conditions will remain isolated.

Strong high pressure north of the islands will continue to
support breezy easterly trade winds across the state through the
rest of the weekend. As a result, AIRMET Tango remains in effect
for moderate mechanical turbulence on the lee side of the
mountains below 9000 ft. This AIRMET is expected to remain in
effect through tomorrow.



Moderate to locally strong trade winds will continue through most
of the week. A slight increase in the trades will occur tonight
and Sunday, as a surface trough passing south of the islands
briefly tightens the local pressure gradient. A Small Craft
Advisory (SCA) has been expanded from the typically windy waters
around the Big Island and Maui to include the Kaiwi Channel and
windward Big Island and Maui County waters. The SCA is trimmed
back to the typically windy waters for Sunday night and Monday as
the trough departs. High pressure anchored north of the state will
produce border line SCA conditions for the typically windy waters
Tuesday and Wednesday with slightly stronger winds expected late
in the week.

The north-northwest swell has declined to 3 to 5 ft at 13 seconds
this afternoon. North shore surf will decline to around average
(about 6 ft) tonight and early Sunday and fade on Tuesday. No
other significant northwest swells are due this week. South shore
surf is holding around September average (around 5 ft). The south
swell will drop slightly on Sunday then fade, leading to mainly
summertime background surf heights through the rest of the week.
Trade wind swell is running at about 5 ft at 8 seconds, which is
near September average. Little change is due through Sunday,
followed by a small decline early in the work week and an increase
back to near average Thursday or Friday.


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

Small Craft Advisory from 6 PM this evening to 6 PM HST Sunday
for Kaiwi Channel-Maui County Windward Waters-Big Island
Windward Waters.




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

This page is maintained voluntarily by the MKWC and the UHMET faculty, staff, and students.
It was last modified on: Wed, Dec 17 2014 - 1841 UTC
Send comments to: Ryan Lyman