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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 131359

Area Forecast Discussion
National Weather Service Honolulu HI
359 AM HST Wed Nov 13 2019

A weak high pressure ridge north of the state will keep light
easterly to southeasterly winds over the region modified by
overnight land breezes and daytime sea breezes through Thursday.
A trend towards wet weather will begin from Friday into Saturday
as a cold front approaches the islands from the northwest and a
trough moves in from the southeast. Unsettled weather will
continue to linger across the state through the first half of
next week.


A weak high pressure ridge over the Hawaiian Islands will keep
weather conditions fairly stable into Thursday. A cold frontal
boundary will remain north of the state. A stronger low pressure
system and cold front will move into the region from the northwest
direction by Friday. Another low pressure system roughly 600 miles
southeast of the Big Island will also move into the Hawaii region
by the end of the week.

Today through Thursday, expect light easterly winds to veer
towards the southeasterly direction on Thursday. Daytime sea
breezes will help build up clouds over island mountain and
interior sections each day with slight chances for shower
activity mainly in the afternoon to early evening hours.
Overnight land breezes will clear out cloud cover over the islands.

Two low pressure systems begin to converge over the state from the
west and the east on Friday. A trend towards a light southerly
winds starts to develop ahead of the cold front approaching the
islands from the northwest. Light southerly winds will interact
with the island land and sea breezes. Precipitable Water (PW)
amounts are forecast to range from 1.5 to 2.0 inches through the
weekend. Rainfall chances begin to trend higher over Kauai and
the Big Island on Friday afternoon as deeper moisture and
instability moves into the western and eastern ends of the state.

On Saturday, medium range weather models are showing a cold front
moving into the western half of the state, while another low
pressure trough moves into the Big Island and Maui. These two low
pressure systems will converge over the state through the weekend
causing a significant increase in unsettled weather conditions statewide.
Confidence in heavy rainfall and thunderstorm activity is growing
as the forecast time period gets closer.

Long range model guidance shows cold air moving in behind the
cold front getting trapped over the islands. This pool of cold air
in the upper levels will cause a cut off low to develop over the
islands for the first half of next week. Expect continued
unstable conditions through next week Monday and Tuesday due to
the unstable dynamics under this upper low. Island by island
impacts will depend highly upon the location and intensity of this
developing upper level system. Stay tuned for weather updates as
this long range forecast will evolve over time.


Winds will be light over this forecast period with nighttime land
breezes and daytime sea breezes expected. Afternoon showers are
possible over inland areas this afternoon. Brief, passing MVFR
conditions are possible in these areas but the rest of the state
should continue with VFR conditions through the forecast period.

There are no AIRMETs currently in effect.


No significant changes to the forecast with this mornings package.
Light winds will continue to prevail, with some easterly
component still felt today. A southerly flow will spread over the
islands during the latter part of the week as a front approaches
from the northwest. Winds are expected to remain well below Small
Craft Advisory (SCA)levels through the end of the week. Winds are
expected to swing around to the east on Sunday and Monday, and
could get close to SCA levels over the typically windy waters
around Maui County and the Big Island.

The current northwest swell will continue to lower today. A
larger north-northwest swell is expected to arrive on Thursday,
peak Thursday night at advisory levels, then lower gradually
Friday and Saturday. A larger northwest swell is expected to
arrive on Saturday, peak Saturday night, then lower gradually
Sunday and Monday. Surf heights may reach low end warning levels
during the peak of this swell.

A series of small southerly swells are expected through the
weekend. Surf will remain small along east facing shores due to
the light winds over and upstream of the state. Surf heights will
likely rise by early next week as high pressure build in to our





MARINE...M Ballard

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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