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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 132003

Area Forecast Discussion
National Weather Service Honolulu HI
1003 AM HST Sun Oct 13 2019

Fresh trades will focus light passing showers over windward slopes
through Tuesday night. A front dropping southward toward the
state and an upper level disturbance passing overhead, will weaken
the trades and bring a chance for some heavier showers to the
area Wednesday through Thursday. More typical trade wind weather
should then return Friday into next weekend, as high pressure
builds north of the island chain.


A 1024 mb surface high is centered far to the northeast is driving
fresh trade winds over the islands this morning. Upper level
ridging over the area is keeping the atmosphere stable. 12Z
soundings show strong inversion from 5500 feet at Lihue to 8000
feet at Hilo. Radar and visible satellite shows low clouds and a
few passing light showers carrying in with the trade winds which
are focused over the windward slopes. Expect these current weather
conditions to continue through Tuesday night.

A more unsettled pattern will develop on Wednesday as a weakening
front pushes into area from the north and with the trades funneling
the associated clouds and showers over the islands through Thursday
according to the GFS. The ECMWF shows a somewhat drier setup with
the front dissipating as it reaches Kauai and the moisture not
making it all the way down the island chain. An upper low will dig
towards the southwest and cross over the state as will act to
enhance the low level moisture in place. Thus, there is the
potential (particularly if the GFS is correct) that some of the
rainfall could be on the heavy side as well. The front will also
weaken the trade winds back to moderate breezes Wednesday through
Thursday, then strengthen again Friday into the weekend. More
typical trade wind weather featuring light windward and mauka
showers will return Friday into next weekend.


Surface high pressure well northeast of the state will allow for
moderate to easterly trades to persist today. This pattern will
bring scattered showers to the windward coasts and slopes with
some isolated activity pushing over the elevated terrain and onto
leeward areas. Partly cloudy with VFR conditions expect elsewhere.

No AIRMETs are currently in effect.


Fresh to strong trades associated with high pressure will hold
through Monday, then lower into the light to moderate category
through the midweek time frame as a dissipating front approaches
the region from the north. A Small Craft Advisory (SCA) is in
place for the typical windier marine areas around Maui County and
the Big Island has through Monday.

A small south-southwest swell filled in overnight and will
continue to persist through Monday. The latest observations from
the offshore and nearshore buoys south of the islands are
reflecting this energy within the 17 and 19 second bands. This
source will trend down by Tuesday. For the long range, recent
satellite data showed a large storm- force low (946 mb) well
southeast of New Zealand that has driven seas into the 30 to 40 ft
range over the past 24-hrs. Although the bulk of this energy was
focused east of the islands, a small to moderate south swell
can't be ruled out locally next weekend.

Surf along exposed west facing shores may trend up tonight
through Monday as a small westerly swell from Tropical Cyclone
Hagibis fills in, which may hold into Tuesday before dropping off.
Some of this energy may wrap into some northern exposures as it
fills in.

Surf along north facing shores will remain small through the first
half of the week, then potentially trend up through the second
half as a northwest swell from recurving Hagibis fills in.
Confidence in the details remains low at this point due to the
fast track of Hagibis over the far northwest Pacific in the next
few days.

Rough and choppy surf will continue along east facing shores
through Monday, then trend down into midweek as the trades ease.


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