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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 261333

Area Forecast Discussion
National Weather Service Honolulu HI
333 AM HST Mon Oct 26 2020

A surface ridge over the islands will produce locally breezy
southeast winds around the Big Island and gentle and variable
winds around the smaller islands through today. Sea breezes will
increase cloud cover across interior sections this afternoon. A
strong upper low north-northwest of the islands may trigger bouts
of heavy rainfall across the western islands tonight through
Thursday. There is a slight chance of thunderstorms statewide from
this morning through Thursday.


A surface ridge to our northeast is driving southeast flow near
the Big Island and Maui. The Big Island and Maui partly block this
flow so winds are gentle and variable over the rest of the
islands. Expect cloud cover to increase across mauka areas of the
smaller islands during the day as heating induces development of
local sea breezes.

An upper low developing north-northwest of the islands is
forecast to drift southward over the next few days. This will
make the atmosphere increasingly unstable. The atmosphere is
already rather moist with PW around 1.4 inches. The atmosphere
will become even more moist as the upper low pulls tropical air
over the islands. While it seems certain that a period of wet
weather for the state will begin tonight and last at least
through Thursday, uncertainty remains concerning where and when
heavy rainfall and thunderstorms will occur. However, with
isolated thunderstorms already firing up at times northwest of
Kauai and near Molokai, the forecast has been changed to include a
slight chance of thunderstorms everywhere from this morning
through Thursday. The threat of heavy rainfall appears to favor
the western islands beginning tonight and last through at least
Thursday, so a Flash Flood Watch is now in effect for Niihau,
Kauai and Oahu for that time period.


A low pressure system and cold front approaching Hawaii from the
northwest will bring periods of showers and MVFR conditions to
the western half of the state over the next several days. Isolated
IFR conditions are also possible in heavy showers along with
isolated thunderstorms. This low pressure system will also keep
light and variable winds in the forecast for all islands. On-shore
sea breezes will form over each island in the day with off-shore
land breezes developing in the overnight hours.

Low cloud ceilings will likely produce Tempo Mountain Obscurations
over the next several days, mainly over the western islands of
Kauai and Oahu.

No AIRMETs currently in effect.


A ridge near Kauai will bring southeast flow across the area with
the strongest winds east of Maui and the Big Island. A front
approaching the area from the west will bring the chance of heavy
rain and thunderstorms through much of the week.

A moderate sized northwest swell has lowered overnight and will
continue to drop through Wednesday. The high surf advisory for
north and west facing shores has been cancelled. Another moderate
size long period northwest swell may arrive late Saturday. A small
northeast swell is expected to fill in today and linger through
Tuesday. There will be a series of small, long period south swells
through the week.


Flash Flood Watch from this evening through Thursday afternoon
for Niihau-Kauai-Oahu.




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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