Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 201339
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
339 AM HST Mon Feb 20 2017

.SYNOPSIS...
Breezy trade winds can be expected through the work week as a
series of high pressure areas build north of the state. Clouds
and showers will favor windward and mauka areas, with showers
spilling over into leeward locations from time to time. Winds
will diminish over the weekend as an area of low pressure
develops northwest of the island chain.

&&

.DISCUSSION...
Currently at the surface, a 1029 mb high is centered around 625
miles north-northwest of Kauai, with a weak and dissipating front
south of the Big Island. This is driving a breezy to locally windy
trade wind flow across the island chain early this morning.
Infrared satellite imagery shows mostly cloudy conditions across
windward areas, with partly cloudy skies in most leeward locales.
Meanwhile radar imagery and rain gauge observations indicate only
very light showers or mist moving into windward areas this
morning, with rain free conditions over leeward locales. Main
short term concern revolves around the breezy to windy conditions
over the next few days.

Today through Wednesday,
A series of high pressure areas will build north of the island
chain through the period, maintaining breezy to locally windy
trades through the period. A dry airmass with precipitable water
(PW) values generally at or below 1 inch will keep shower activity
light and limited primarily to windward and mauka areas through
tonight. A bit of an increase in windward and mauka showers
is expected Tuesday through Wednesday as an upper level trough
moves overhead. This will result in rising inversion heights and
sending some light showers into leeward areas from time to time.

The mid and upper level cloud cover has cleared Oahu and Kauai,
with the thinning band of mid/high clouds currently moving
through the eastern islands. Overall, partly to mostly cloudy
skies are expected in windward areas through the period, with
clear to partly cloudy skies in leeward locales.

The current Wind Advisory remains remains in effect for Lanai,
Kahoolawe, and for areas over and downwind of the Kohala mountains
on the Big Island through 6 PM this evening. Winds have increased
in areas south of Volcano overnight, so the advisory has been
expanded to include this area as well through 6 pm. Winds are
expected to drop below advisory levels in these areas tonight.

Wednesday night through next Sunday,
High pressure north of the state will keep moderate to breezy
trade winds in place through Friday, with the trades diminishing
over the weekend as an area of low pressure develops to the
northwest of the island chain. A dry airmass will remain in place
across the state for the tail end of the work week and through
next weekend, with PW values remaining at or below 1 inch. As a
result, showers should remain limited primarily to windward and
mauka areas through the period. There may be an increase in
showers by early next week as some tropical moisture begins to
work its way northward from the Intertropical Convergence Zone
(ITCZ). Confidence remains low regarding the exact details at this
time given considerable disagreement between the reliable model
guidance.

&&

.AVIATION...
A strong high pressure system located north of the islands will
continue to produce strong and blustery northeast trade winds
through most of the new week. Also, a strong low level inversion
is slated to be based between 45 hundred and 6k feet at least
through tonight. These two features will produce tempo moderate
turb below 8k feet.

Turbulence models were suggesting a bit of mid to high level
turbulence between 18k and 30k feet mainly over the central
islands. This area of turb should be easing off by the next
aviation package (16Z).

Remnant moisture from a front has eased up on windward Big Island.
Thus AIRMET Sierra for mountain obscuration was lowered around
midnight. There is plenty of low clouds coming in with the
northeast trades. However, these clouds appear to be high based
around 45 hundred feet.

With the northeast trades in place, scattered light showers are the
rule-of-thumb favoring the windward and mountain areas of all of the
larger islands. Expect some brief MVFR ceilings with these showers.
Restriction to vis from the showers is not expected. Otherwise,
VFR is the prevailing flying condition. A band of mid to high
level clouds continue to thin as it passes through the eastern
part of the island chain.

No other AIRMETs are expected.

&&

.MARINE...
The Sunday evening ASCAT pass did not find any gales in the
Alenuihaha Channel, but did find some areas of 30-32 kt winds,
and high-resolution models suggest that winds may increase a bit
more today in the typically windy zones around Maui County. Thus
the Gale Warning will remain posted through today for the Pailolo
and Alenuihaha Channels and Maalaea Bay. Small Craft Advisory
conditions will continue for all other waters due to the
combination of strong winds and high/rough seas, and the advisory
has been extended for those waters through Tuesday. The areas
currently in the Gale Warning will need to be added to the
advisory as well once the gales end.

In addition to the winds and rough seas, a north-northwest swell
will remain near peak levels into this morning, then gradually
ease later today through Tuesday. Significant wave heights at
the nearshore buoys and at buoy 51101 are running somewhat above
the latest wave model guidance. This swell will continue to
produce advisory-level surf along north and west facing shores of
the smaller islands today. With swell rising well above guidance
levels at the Hilo buoy, we have decided to err on the side of
caution and add the north facing shores of the Big Island to the
high surf advisory for today as well.

Surf along east facing shores will gradually rise through
midweek, and may reach advisory levels by Tuesday night or
Wednesday.

On Wednesday, a moderate, long-period west-northwest swell
associated with a developing gale east of Japan is expected to
fill in, peaking late Wednesday through Wednesday night. This
swell will gradually ease Thursday, before a reinforcing swell
from the same direction, but longer period, builds in late
Thursday night and Friday. If this source comes in slightly
higher than predicted, advisory-level surf along north and west
facing shores will be possible Wednesday and Wednesday night.
Advisory-level surf looks more likely with the Friday swell
event.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Molokai-Maui
Windward West-Maui Central Valley-Windward Haleakala-Big Island
North and East.

Wind Advisory until 6 PM HST this evening for Lanai-Kahoolawe-
South Big Island-Big Island North and East-Kohala.

Small Craft Advisory until 6 PM HST Tuesday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Maui County Leeward Waters-Big Island
Windward Waters-Big Island Leeward Waters-Big Island Southeast
Waters.

Gale Warning until 6 PM HST this evening for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel.

&&

$$

DISCUSSION...Jelsema
AVIATION...Lau
MARINE...Jacobson


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