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Temp3.1 C
RH89 %
WindSSW 3 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 190216

Area Forecast Discussion
National Weather Service Honolulu HI
416 PM HST Wed Jul 18 2018

High pressure north of the state will drive breezy trade winds
into Thursday. A few windward showers will linger through the
night, but drier weather will spread across the islands through
Thursday. Winds will taper off to moderate breezes Thursday night
and continue through the weekend.


Surface analysis depicts two 1033 mb highs about 1800 miles
northeast and northwest of Honolulu. Meanwhile, a surface trough
is located about 500 miles south of Honolulu and moving west. The
tight pressure gradient between these features is producing a
breezy trade wind pattern over the islands, which will continue
through Thursday as the trough weakens and moves away to the west.
Aloft, water vapor imagery depicts a narrow but strong midlevel
ridge sitting over the state maintaining stable atmospheric
conditions. An upper level trough to the northwest will drift
closer to Kauai and keep areas of high clouds streaming overhead

Radar shows much of the showers that moved in last night from the
passing surface trough to the south have dissipated, but a few
lingering showers remain across windward Kauai this afternoon. 00Z
soundings show increasingly stable but moist conditions over the
state this afternoon. Precipitable water (PW) of around 1.6 inches
was recorded at Hilo and Lihue with an elevated midlevel
inversion. MIMIC-TPW satellite imagery depicts an incoming drier
airmass with estimated PW values below 1.4 inches about 50 miles
east of the Big Island moving steadily westward. This drier
airmass will push across the state tonight allowing for dry and
pleasant conditions that will continue over the next several

Trades will weaken to moderate breezes Thursday night and continue
through the weekend. Passing mainly light showers will focus over
windward areas. Heading into early next week, the last couple of
GFS runs have come into much better agreement with the ECMWF in
keeping deeper moisture associated with the next westward moving
tropical disturbance suppressed mainly to the south of the state.
Therefore have lowered rain chances somewhat for Sunday and
Monday. Another wave of tropical moisture may approach the state
from the southeast by the middle of next week.


Strong high pressure to the north of Hawaii will keep breezy
trade winds in place through Thursday. AIRMET Tango for low-level
turbulence is in effect for turbulence below 8000 ft south and
west of mountains and should stay in place through Thursday.

VFR conditions are expected through this period in most areas
except for small pockets of possible MVFR conditions on the
windward side of the mountains. With more moisture expected to
move across the Big Island, there is a better chance for MVFR
conditions and an AIRMET for mountain obscurations may eventually
be needed. Will monitor closely and update as necessary.


A surface trough is currently passing south of the state and is
causing locally fresh to strong trade winds. As a result, a Small
Craft Advisory (SCA) is in effect for the typical windy waters
around the Big Island and Maui County and the waters around Oahu.
Winds will decline a notch Thursday and Friday, and the SCA will
likely be scaled back to the typically windy waters through the

Local PacIOOS buoys have recently been registering seas of 8 to 10
ft at 8 to 10 seconds. Thus, a High Surf Advisory (HSA) is in
effect for east facing shores through tonight. As winds decline
Thursday and Friday, east shore surf will drop back to seasonable

A series of reinforcing south and southwest swells will maintain
small to moderate surf along south facing shores across the state
through Friday. Slightly larger and longer period south-southwest
swells spreading across the state this weekend may cause surf to
approach the HSA threshold along south facing shores from Saturday
into Monday.

See the latest Oahu Surf Discussion (SRDHFO) for additional details
on surf and swell.


High Surf Advisory until 6 AM HST Thursday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-South Big Island-Big Island North and East.

Small Craft Advisory until 6 PM HST Thursday for Kaiwi Channel-
Maui County Windward Waters-Maalaea Bay-Pailolo Channel-
Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

Small Craft Advisory until 6 AM HST Thursday for Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Maui County Leeward



MARINE...Kino/M Ballard

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office