Area Forecast Discussion
Issued by NWS Honolulu, HI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
000
FXHW60 PHFO 201330
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
330 AM HST Fri Apr 20 2018

.SYNOPSIS...
Wet weather and cloudy skies will remain in place through today,
particularly over windward areas. Some showers may be heavy at
times and isolated thunderstorms are possible. A typical trade
wind pattern will return tonight, with showers favoring windward
and mauka areas. High pressure north of the state will maintain
moderate to breezy trade winds through the weekend, before
strengthening to locally windy levels next week.

&&

.DISCUSSION...
An upper level trough across the main Hawaiian Islands has
destabilized our airmass, while an old frontal boundary embedded
within trade flow supplies low level moisture from the east. This
combination warrants continuation of a flash flood watch through
this afternoon. Mostly cloudy to overcast conditions will prevail
across the state, with an extensive shield of mid and high cloud
currently extending well southwest of the island chain. These
layered clouds are pushing east, raising chances of winter
weather at the Big Island summits. A winter storm warning has been
extended there through tonight.

Radar shows showers pushing into windward areas at this hour, with
some of these showers becoming briefly heavy across windward
sections of Kauai, Oahu and Maui. Models show continued trade
flow through the forecast period, so showers will continue to
favor windward and mountains areas. However, leeward locations
will get wet as well from time to time. The upper trough will push
eastward across the islands through today, maintaining the
possibility of heavy rainfall and thunderstorms. By this evening,
drier air from the east and increasing stability will gradually
decrease shower intensity and coverage.

A surface ridge to the north will maintain moderate to locally
breezy trade winds tonight through the weekend. High pressure
will strengthen Monday bringing trades to locally windy levels
through Wednesday. Overall, a fairly typical trade wind pattern is
expected through the period, with bands of enhanced clouds and
showers drifting through the islands from time to time. Showers
will focus over windward and mauka areas with some showers riding
the strong trades to leeward locations.

&&

.AVIATION...
A ridge of high pressure north of the state will keep a moderate
trade wind flow in place through tonight. Abundant moisture over
the state along with an upper level trough moving overhead will
result in showery weather this morning in windward areas with
conditions improving from northwest to southeast down the island
chain this afternoon. Widespread MVFR cigs/vsbys are expected
this morning for windward areas, with VFR conditions then
developing from northwest to southeast down the island chain this
afternoon. Predominantly VFR conditions are expected tonight,
with some MVFR cigs/vsbys possible across windward sections of
Maui and the Big Island.

AIRMET Sierra remains in effect for mountain obscuration over
north thru east sections of Kauai, Oahu, Molokai, Maui and the
Big Island. These conditions are expected to continue through the
morning, with improving conditions this afternoon.

AIRMET Tango remains in effect for low level turbulence below 100
over and downwind of the terrain of all islands. These conditions
will likely continue through the day. AIRMET Tango is also in
effect for moderate upper level turbulence between FL250 and
FL450 due to a jet stream in the vicinity of the islands. This
AIRMET will likely remain in place through Saturday.

AIRMET Zulu remains in effect for moderate icing between 120 and
FL250 from Molokai eastward to the Big Island. These conditions
are expected to continue through the morning, although some
improvement is possible over the Maui County islands.

&&

.MARINE...
A surface high north of the area will move northeast through
Saturday. The high is producing locally strong trade winds over
Hawaiian waters, but a trough aloft is keeping winds weaker than
might be expected. The trough will bring a slight chance of
thunderstorms with locally heavy downpours today.

A Small Craft Advisory (SCA) continues through early Saturday
morning for strong trade winds in the windier areas near Maui
County and the Big Island. A new high building northwest of the
area will cause the trade winds to strengthen starting this
weekend. The SCA will likely be extended and expanded.

Surf is expected to remain below High Surf Advisory (HSA)
thresholds along all shores through this weekend. Rough surf will
persist along east facing shores through Sunday night due to the
trade winds, but heights will remain moderate through the weekend.
As trade winds strengthen early next week, surf may approach the HSA
threshold.

A moderate northwest swell is expected to build today. A slightly
larger swell will peak Sunday and another moderate swell is
possible next Thursday.

A series of small swells from the southern hemisphere will maintain
modest surf along south facing shores chain through this weekend.
Lows in the southern hemisphere may strengthen and shift east
enough to produce some bigger surf along south facing shores by
the end of next week.

See the Collaborative Surf Discussion for additional details on
surf and swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through this afternoon for Niihau-Kauai-Oahu-
Molokai-Lanai-Kahoolawe-Maui-Kona-South Big Island-Big Island
North and East-Kohala-Big Island Interior.

Winter Storm Warning until 6 AM HST Saturday for Big Island
Summits.

Small Craft Advisory until 6 AM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Powell
AVIATION...Jelsema
MARINE...Donaldson



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.