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Temp5.4 C
RH12 %
WindE 15 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 230151

Area Forecast Discussion
National Weather Service Honolulu HI
351 PM HST Fri Jun 22 2018

A strong high pressure system will pass through the Central
Pacific basin this weekend reinforcing the ridge north of the
islands and producing breezy to locally windy trade winds through
next week. Expect typical windward and mauka clouds and showers
with brief periods of showers passing through leeward areas.


Clouds and showers continue to drift through the region today
favoring windward and mauka areas. A strong high pressure center
far north of Hawaii will move eastward across the Central Pacific
basin this weekend reinforcing the high pressure ridge roughly
1200 miles north of the Hawaiian Islands. Water vapor satellite
imagery shows a weak upper level low just east of the state, this
low will drift over the islands on Monday. This low center
remains fairly weak with little impacts to our weather pattern.
The ridge north of the islands will produce deep east to
northeasterly trade winds over the state through at least next
week Friday.

The upper air soundings this afternoon show the trade wind
subsidence inversion at around 8,000 feet, the inversion height
will cap cloud heights, and periodically range up to 10,000 feet
through the week. The trade wind inversion heights in the 8,000
to 10,000 foot range is high enough to support likely showers
along windward an mountain slopes with brief periods of showers
passing over leeward sections of each island through the week.

Models are in good agreement with this high confidence summer
trade wind weather pattern. Breezy trade winds will continue to
push vog (Volcanic smOG) emissions south of the smaller islands.
Any volcanic ash from Kilauea and the East Rift Zone vents will
likely drift towards the southwest over the Kau district.


Strong trade winds will continue into this weekend as high
pressure builds far northeast of the state and drifts eastward.
VFR will prevail over most sections of the islands, with brief
MVFR conditions likely in windward and mauka areas in passing

AIRMET SIERRA is no longer in effect for mountain obscuration on the
Big Island. AIRMET Tango remains in effect for low level turbulence
over and SW of all islands.


A 1030 mb surface high about 1300 nm NW of the islands will move
E and strengthen, passing far N of the islands as a 1035 mb high
on Saturday. The high will continue to move E with little change
in central pressure through early next week, and then remain in
its climatological position far NE of the area for much of next

Although the high will pass far N of the islands (moving E along
40N), and a front will lie between the islands and the high, trade
winds are expected to strengthen through Saturday, and remain
fresh to strong into Monday. A subtle dip in the winds early next
week may precede another slight increase around the middle of the
week as the high wobbles around to the distant NE. A Small Craft
Advisory is in effect for the windier areas, and may need to be
expanded to include other zones as winds peak this weekend.

Short-period wind waves driven by the local and upstream trade
winds will bring increasing surf to E facing shores into Sunday,
with peak surf heights expected to approach, but remain below,
advisory level heights into early next week. Persistent trade
winds in the SE Pacific will send a small short-period swell
toward the islands from the SE, but the Big Island tends to shadow
the other islands to some degree. Otherwise not much in the way
of long-period swell is expected until the middle of next week,
when a new S swell is expected to arrive, producing surf near
advisory levels along S facing shores around Thursday. The updated
Oahu Surf Discussion (SRDHFO) contains additional details.


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

Small Craft Advisory until 6 PM HST Saturday for Kaiwi Channel-
Maui County Windward Waters.




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