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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 081955

Area Forecast Discussion
National Weather Service Honolulu HI
955 AM HST Mon Aug 8 2022

Moderate to locally breezy trade winds are expected to prevail into
next weekend, but may become locally windy around the middle of the
week as a tropical disturbance passes south of the area. Clouds and
brief showers will focus over windward slopes and coasts, with
afternoon and evening clouds over leeward Big Island slopes.


Seasonable trade wind weather is expected through the forecast
period, with persistent high pressure far NE of the islands
supplying a steady trade wind flow. Winds may increase around the
middle of this week as surface pressures lower to the S of the
islands, with a tropical disturbance potentially developing within a
broad area of low pressure. A tightening of the local pressure
gradient is expected, with locally windy conditions possible, but
there continues to be a greater than normal amount of uncertainty
with this forecast, as global model guidance appears to be
overestimating the strength of the disturbance. There is also a
chance that shower coverage will increase near the Big Island
Wednesday and Thursday as a result of the disturbance's passage.
Winds will ease slightly toward the end of the week as the
disturbance moves quickly westward away from the area, with moderate
to locally breezy trade winds expected into next weekend. Long term
guidance indicates a trend toward lighter winds early next week.

A mostly dry trade wind weather pattern is expected to prevail, as a
mid- and upper-level ridge extends over the area from a high
centered to the NE of the islands. Little change to the ridge's
strength is expected through Friday as it moves slowly N, while some
weakening of the ridge may occur next weekend. A strong subsidence
inversion will limit shower coverage and intensity, with brief
showers primarily favoring windward areas, although leeward Big
Island will receive afternoon and evening showers. In the short
term, clouds and showers will be a little more widespread over
windward Big Island, with some of these spreading to windward Maui

A jet max associated with a low aloft NW of Kauai is sending some
cirrus clouds northeastward near Kauai, but the low is forecast to
move N over the next couple of days, and most high clouds will lift
N of the area. Some increase in mid- and high-level clouds is
possible Thursday and Friday as a new low aloft develops NW of
Kauai, with southerly flow aloft potentially advecting some moisture
over the islands from the tropics.


High pressure well northeast of the state will strengthen trade wind
flow over the next several days. A dry airmass across the islands
through Tuesday will limit the areal coverage of showers, however
strengthening trades will focus clouds and showers along favored
windward and mauka areas. Mainly VFR conds are expected across most
TAF locations into Tuesday. However MVFR cigs will occasionally
drift across windward Big Island this morning, continuing the need
for AIRMET Sierra due to tempo mountain obscurations.

Additionally, AIRMET Tango continues as locally breezy trades
generate low level mechanical turbulence downwind of the mountains.


The gradient around the southern periphery of northeast Pacific high
pressure is being enhanced by an area of broad low pressure
positioned well southeast of the islands. This is driving locally
strong trades in the typical windier locations around Maui County
and the Big Island this morning. The Small Craft Advisory remains in
effect for these areas with no changes needed. Moderate to fresh
trades will then become established around Oahu and Kauai during the
next 18 to 24 hours as this area of low pressure slowly advances
westward. An expansion of the SCA may eventually be required by late
Tuesday or early Wednesday, especially if trades further strengthen
in response to any increased organization or developing low pressure
within this trough.

Strengthening trades will build short-period wind waves over east-
facing shores through mid-week, peaking near or slightly above the
seasonal average Wednesday into Thursday. A very small, long period
south swell arrives tonight into Tuesday, fading by Thursday. No
significant swell is expected through the forecast period.


Small Craft Advisory until 6 AM HST Thursday 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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
Send comments to: Ryan Lyman