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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 242015

Area Forecast Discussion
National Weather Service Honolulu HI
1015 AM HST Mon Oct 24 2016

High pressure north of the state will maintain moderate trade
winds through mid week. The trades will strengthen late in the
week and remain strong through the weekend. Showers will favor
windward and mountain areas with an increase in showers expected
as the trade winds increase.


High pressure far to the north is propelling island trade winds at
moderate speeds with breezy conditions throughout the state. An
old frontal band is bringing clouds and showers to windward areas
from Maui to Oahu this morning with some showers reaching leeward
locations. This band will sag to the south through the day and
into tonight bringing increasing clouds and showers to Big Island
windward areas later today, maintaining windward showers over
Maui County, and partially clearing over Oahu this afternoon. The
cloud band will clear south and west of the Big Island by tomorrow
morning. A similar frontal band will bring clouds and showers
Wednesday and Wednesday night as it passes from northeast to
southwest through the island chain.

The high pressure will maintain moderate trade winds through
midweek with limited showers focusing over windward and mountain
areas with passing leeward showers over the smaller islands. The
leeward Big Island will continue to see a diurnal pattern of
increasing afternoon clouds with scattered showers forming over
the slopes.

Trade winds will ramp up for the second half of the week as the
high pressure to the north strengthens and sinks south. Expect a
jump in the windspeeds between Wednesday and Thursday with breezy
conditions and strong gusts. Strong trades will continue through
the weekend as the high remains in place.

Upper level ridging will keep a cap on showers through Friday
afternoon with light to moderate rainfall amounts expected within
trade showers. An upper level trough is expected to push the ridge
to the south later on Friday and bring cooler temperatures aloft
over the islands. The cooler temps will increase instability and
allow for increased shower coverage and intensity Friday night and
into the weekend. With the strong trades and increasing cloud
growth, expect a wet trade wind regime to continue into next week.


AIRMET TANGO for low level turb over and immediately south through
west of the mountains remains posted. High pressure north of the
state continues to support breezy trade winds. Pockets of 25 KT
winds continue to pop up on the VAD wind profiles, and PIREPS this
morning have noted the presence of MOD turb. The 12Z soundings
show a strong low level inversion to be near 6.5 kft. The chance
for low level turb will diminish into this evening as the high
north of the state weakens and winds ease up slightly.

AIRMET SIERRA is posted for mountain obscuration over the north
and east facing slopes on Maui, Molokai, and Oahu. An area of
enhanced clouds and showers from Oahu to the Big Island, will
continue to push west through the islands today. Prolonged
periods of MVFR will be likely along the windward areas today.
AIRMET SIERRA may be needed to be expanded to the Big Island as
the clouds and showers push west. Trade winds will carry some
showers to leeward areas.


The overnight ASCAT pass that came in around midnight showed 20 to
30 knot trade winds over the Hawaiian waters. The highest winds were
located over the typically windier locations between Molokai and the
Big Island and south of Oahu. The latest numerical guidance has
initialized well with the current pattern and generally depicts a
downward trend today through Tuesday. As a result, the small craft
advisory will be updated to only include these windier locations
between Molokai and the Big Island today through Tuesday. High
pressure will build north of the state once again later in the week
and will result in a return of strong trades. Another period with
gales in the windier marine zones and advisory-level surf along east
facing shores will become a possibility over the weekend.

The latest CDIP/PacIOOS nearshore buoy observations exposed to the
strong trades have also begun to show a downward trend and all
remain below the 10 ft advisory-level. That trend will continue
through Tuesday. The surf along east-facing shores will respond
and steadily ease with values remaining below advisory levels.

A new long-period northwest swell will fill in later tonight, peak
late Tuesday through Tuesday night, then gradually ease later
Wednesday through Friday. Surf heights will respond, but should
remain well below advisory levels through the peak. A small south
swell has recently begun to fill in at the Lanai buoy, which should
translate to a slight increase in surf along south facing shores
today through Tuesday before fading through the mid-week period.


Small Craft Advisory until 6 PM HST Tuesday 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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