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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 170627

Area Forecast Discussion
National Weather Service Honolulu HI
827 PM HST Sun Feb 16 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 with
increasing shower trends are forecast through the middle of the


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.


Expect breezy trade winds through this forecast period and beyond.
The northeast sustained winds 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 pass from W to E well N of the islands
this week, supporting fresh to strong trade winds the next couple
of days. Expect a general increase in trade wind speeds through
about Wednesday/Thursday, when winds are expected to peak near
gale force, 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
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 remains in place tonight as near shore
buoys are indicating combined seas near 10 feet and an earlier
ASCAT pass showed areas of 25 kt winds over waters N of Maui and
Molokai. A brief drop in seas may allow this SCA to be trimmed
Monday, but winds and seas trending back up by late Tuesday will
likely require a SCA for all zones until winds and seas trend down
toward the end of the week.

High surf is likely along E facing shores of most islands as winds
and seas increase, 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 Tuesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory until 6 AM HST Monday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Maui County Leeward Waters-Big Island Windward 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