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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 171348

Area Forecast Discussion
National Weather Service Honolulu HI
348 AM HST Mon Feb 17 2020

A ridge of high pressure north of the state will bring breezy
trade wind weather through the week. Clouds and passing showers
will favor windward and mountain areas, with most leeward
locations remaining mostly dry. Stronger trade winds in the breezy
to windy range with increasing shower trends will develop from
Tuesday through Thursday.


A high pressure ridge north of the state will keep moderate to
breezy trade winds in the forecast through Friday. The weather
pattern remains unchanged from previous forecasts with isolated
to scattered showers expected over windward and mountain sections
of each island. The higher shower coverage in this range will
occur in the overnight to early morning hours. Leeward areas will
see drier conditions with isolated light sprinkles possible.

Medium range guidance continues to show a change in the weather
from Tuesday through Thursday as a strong high pressure system
moves into the Central Pacific basin. Trade wind speeds will
increase potentially exceeding wind advisory thresholds on
Wednesday and Thursday. A few weak upper troughs will move into
the region, lifting the trade wind inversion height into the 8000
foot range. Stronger winds and weak upper level forcing from the
trough will result in periods of numerous showers along windward
and mountain slopes with more scattered shower activity over
leeward areas. The highest rainfall amounts will favor the
overnight and early morning hours.

The long range forecast guidance shows lighter trade winds by
next weekend as another cold front moves into the region northwest
of the islands. This cold front will dissipate as it passes north
of the state on Sunday and Monday, with unstable bands of showers
associated with the frontal remnants drifting back over the
island chain sometime in the first half of next week.


Breezy trade winds are expected over the next several days. The
northeast sustained trade winds for today are strong enough to
create tempo moderate low level turbulence over west through south
areas downwind of the mountains. The windward slopes will see
brief periods of clouds and isolated showers creating MVFR
conditions. Expect VFR conditions over the rest of the state.


A strong surface high will track eastward well N of the islands
this week, supporting gradually increasing trade wind speeds
through Wednesday/Thursday. Fresh to strong trade winds are
expected into Tuesday, with winds peaking near gale force by
midweek, especially where most accelerated by island terrain.
Winds are expected to trend down heading into next weekend as the
high moves into the NE Pacific, and a front approaches the
islands from the NW. No significant weather features are expected
for at least the next several days, with brief trade showers most
active over windward waters during nights and mornings.

A Small Craft Advisory (SCA) for the windier areas around Maui
county and the Big Island will remain in place for most of the
week, except when potentially replaced by a Gale Watch and/or
Warning. A SCA for most other zones has been dropped with this
morning's forecast package, but will likely need to be re-issued
by tonight or Tuesday, then remain posted until winds and seas
trend down toward the end of the week.

High surf is likely along E facing shores of most islands as seas
increase in response to the increased winds, most likely from
late Tuesday through Thursday. Surf along N and W facing shores
will remain below advisory levels through the week, with the
largest NW swell over the next week expected to peak below
advisory levels next weekend. In the meantime, a mix of swells
from the NNW, NW and NNE will keep surf from going flat, with a
small-to-moderate long-period NW swell expected around Wednesday/
Thursday. Surf along S facing shores will remain above the
seasonal average into Tuesday, as an out of season S swell moves
through. Long range model guidance is indicating a large NW swell
in about 7-9 days.


Small Craft Advisory until 6 PM HST Wednesday for Kaiwi Channel-
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
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