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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 251415
Area Forecast Discussion
National Weather Service Honolulu HI
415 AM HST Tue Jul 25 2017
As the last of the remnants of Fernanda moves out, a more
comfortable trade wind regime continues to settle in. And this
regime will persist into the upcoming weekend. A broad high
pressure cell located far NE of the islands will maintain this
trade wind pattern through the rest of the week, assisted by mid
level ridging. A boost in the trade showers may come on Friday and
Friday night as a band of showers is slated to move through.
Otherwise, showers riding in with the trades will favor the
windward and mountain areas, especially the nights and mornings.
Lee areas of the smaller islands will be dry. Leeward Big Islands
will get their usually afternoon and evening clouds and scattered
The trade winds with a drier air mass continues to spread westward
across the island chain this morning. Dew points in the mid to
upper 60's have reached Maui County, and should be reaching Oahu
shortly. It is expected to reach Kauai by mid morning, nudging
out the last of Fernanda. With the trade winds back, so are the
trade showers. They will be most frequent during the nights and
mornings. Satellite imagery shows the scattered showers are
embedded in a huge sheet of stable stratocumulus clouds that is
just about to cover the entire windward Big Island coast, and is
advancing onto windward Maui. Do not know how far west this field
will advance but once the sun comes up, the field will start
breaking up. Once the sun starts going down, however, the clouds
will begin increasing.
The upper level trough that aided with the flare ups of thunderstorms
early Monday morning is still some 200 miles west of Kauai. However,
the models are weakening it today and thus, it will not be a factor
to our local weather. Mid level ridging will help keep the air
mass stable across the islands to about Thursday.
Strength-wise, the return of the trades will be that of moderate
to locally strong at first. The trades then drops off slightly to
moderate speeds on Thursday. This is due to surface high becoming
slightly weaker from 1031 mb to 1029 mb some 1300 miles NE of the
islands. It is expected to remain at moderate speed into the
upcoming weekend. But there is an outside chance that the trades
may bump up to locally strong late in the weekend.
The GFS solution points to another upper level trough digging 300
miles west of Kauai this Friday. It will likely bring a threat of
thunderstorms to the offshore waters west of Kauai that day. At
the same time, the marine layer deepens from 8 to 10k feet to 10
to 15k feet across the island chain as a band of clouds and
showers, possibly remnants of an old front, to move through the
islands between Friday and Saturday morning. Nice trade wind
weather should return by Saturday afternoon.
Moderate to locally strong northeasterly trade winds are
returning to the islands bringing drier and more stable air to
the region. Expect mostly VFR conditions with scattered showers
over northeastern slopes of all islands, isolated shower activity
There are no AIRMET's currently in effect. However, stronger
winds may produce low level turbulence over and downwind of
mountain ranges by this afternoon.
Trade winds will strengthen as a weak trough west of Kauai moves
away and high pressure builds in. A Small Craft Advisory is
currently in effect and will continue through Wednesday night for
the typically windy zones around Maui County and the Big Island as
trade winds become fresh to locally strong. The high to the
northeast is expected to weaken Thursday, and this will result in
slightly weaker trades that will last through the weekend.
The surface trough has move a safe distance from Kauai where
thunderstorms are no longer a threat to the coastal waters west
through north of Kauai. Thunderstorms however, will remain a
threat to the offshore waters west through north of Kauai today.
There are presently active thunderstorms in progress in this
No significant swells are expected through the week. Surf will
likely remain below high surf criteria on all beaches.
Small Craft Advisory until 6 AM HST Thursday for Maalaea Bay,
the Pailolo and Alenuihaha Channels, and waters south of the
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office