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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 240628

Area Forecast Discussion
National Weather Service Honolulu HI
828 PM HST Sun Oct 23 2016

High pressure north of the state will keep a moderate to locally
breezy trade wind flow in place through mid week. The trades will
strengthen late in the week and next weekend as another strong
high builds north of the island chain. Bands of enhanced moisture
will occasionally move through the area, increasing shower
activity particularly over windward and mauka locales.


Currently at the surface, a 1025 mb high is centered around 750
miles north-northwest of Kauai, and is driving the moderate to
locally breezy trade winds across the area this evening. Infrared
satellite imagery shows partly cloudy skies in most areas this
evening, with some enhanced cloud cover associated with an old
front noted just upstream of the islands. Meanwhile, radar imagery
shows scattered showers moving in with the trades, primarily
limited to windward areas at the moment. Main short term concern
revolves around rain chances overnight.

Moderate to locally breezy trade winds will continue overnight as
high pressure north-northwest of the area remains nearly
stationary. MIMIC total precipitable water (PW) imagery shows a
slight increase in moisture associated with an old front just
upstream of the islands, with PW values between 1.1 and 1.3
inches. This band of enhanced moisture will move into Kauai and
Oahu later this evening and into Maui County and the Big Island
after midnight, resulting in an increase in shower activity
particularly over windward and mauka areas. Given the stable
conditions in place and limited available moisture, rainfall
amounts are expected to remain light.

Monday through Wednesday night,
High pressure to the north-northwest of the state will weaken
slightly through mid week, but the gradient will remain strong
enough over the islands to keep moderate to locally breezy trade
winds in place across the area. A series of enhanced moisture
bands or old frontal remnants will periodically move through the
area, increasing shower activity mainly over windward and mauka
locales. One band of moisture will shift southward through Maui
County and the Big Island on Monday, followed by another band
sinking southward and mainly affecting Kauai Monday night and
Tuesday. A better defined moisture band will then shift southward
through the islands Wednesday and Wednesday night as strong high
pressure begins to build north of the area. PW values through the
period will remain near to below normal, and with upper ridging
keeping conditions stable, rainfall amounts are expected to remain

Thursday through next Sunday,
The trades will strengthen to breezy and locally windy levels late
in the week and through the weekend as strong high pressure builds
to the north of the Aloha state. Upper level troughing will begin
to shift southward toward the state Thursday night and Friday,
with the troughing lingering over the islands through much of
next weekend. The more unstable conditions associated with the
troughing aloft, along with PW values rising to above normal
levels, should result in periods of wet trade wind weather.
Showers will favor windward and mauka areas, but the showers will
reach leeward areas more frequently due to the elevated moisture
levels, more unstable conditions and strong trades.


Gusty trade winds will slowly ease through Monday. AIRMET TANGO
for low level turb over and immediately south through west of the
mountains remains in effect overnight, and will probably be needed
on Monday as well. An upper level jet streak over and east of the
state is also occasionally producing moderate upper level turb
between FL330 and FL360. This AIRMET was dropped earlier, but may
be needed again overnight if further turb reports are received.

Trade winds will continue to focus clouds and showers along the
windward slopes. Some showers will produce periods of MVFR
CIGS/VIS, with an increase expected during the night. VFR
conditions will prevail elsewhere.


A Small Craft Advisory remains posted for most Hawaiian coastal
waters due to the strong trade winds. With the expected gradual
decrease in trade winds over the upcoming days, some zones will
gradually drop out of advisory status later tonight while
remaining up at least through Monday for the typically windy
waters around Maui County and The Big Island.

A High Surf Advisory remains posted along east facing shores due
to elevated surf created by the strong trade winds. Surf will
gradually lower over the next couple of days as the trade winds
decrease. A moderate size northwest swell is expected to arrive
Monday night, peak late Tuesday and Tuesday night, then lower
gradually Wednesday and Thursday. There will also be a series of
small southerly swells throughout the forecast period.


High Surf Advisory until 6 AM HST Monday 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 Monday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory until 6 AM HST Monday for Kauai Northwest
Waters-Kauai Leeward Waters-Kauai Channel-Oahu Windward Waters-
Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters.




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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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