Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 310217 RRA

Area Forecast Discussion
National Weather Service Honolulu HI
348 PM HST MON MAY 30 2016

High pressure building north of the area will support moderate trade
winds for the next couple of days. The high will push moisture
associated with a front over the islands through Wednesday. While
clouds and showers will be most frequent over windward areas, a few
showers will spread to leeward areas. Trade winds will diminish by
the end of the week, with light and variable winds expected again
next weekend.


Clouds and showers associated with a weak cold front have been
moving across the islands from Kauai to Molokai today, and are on
the verge of moving into Maui. The expectation for tonight is that
the front will continue to move slowly S/SE, with windward showers
fairly active from Kauai to Maui. Afternoon soundings show the
boundary layer moisture extends up to 10 kft, with a subsidence
inversion noted near that height. With moisture extending this high,
there could be a few briefly heavy showers along windward areas. A
couple of rain gages have alarmed today, with rainfall rates
briefly reaching one inch per hour.

The forecast calls for high pressure now centered about 850 miles
NNW of the islands to move slowly E through Tuesday, and then
gradually weaken from Wednesday through Friday N of the islands
along 30N. The high will continue to help push the frontal boundary
S and SE down over the island chain, with recent GFS guidance
indicating that this will occur faster than previously forecast.
Given latest satellite trends and the fact that ECMWF guidance shows
an even faster motion than the GFS, the official forecast now
indicates the moisture will spread to the Big Island by Tuesday
night, with the increased moisture associated with the front
explicitly noted in POP grids through Wednesday night. Windward POPs
are still fairly high through Thursday, but the feature itself is
now expected to wash out a little sooner.

Latest guidance continues to indicate that another surge in low-
level moisture and winds will occur N of the front later tonight
into Wednesday, helping to energize the boundary and lead to greater
shower coverage. A mid-level shortwave is also forecast to pass over
the area at this time, and this feature is also expected to aid in
re-energizing clouds and showers along the boundary. Moisture is
still expected to remain confined to the lowest 12 kft of the
atmosphere, but if it were to train over a particular area for a
prolonged period of time, some localized flooding issues could

As the surface high to the N weakens and dissipates Friday into next
weekend, winds over the islands will once again become light and
variable. Although it`s too early to have confidence in the details
of the forecast, current forecast grids indicate a land/sea breeze
weather regime, with clear skies nights and mornings giving way to
afternoon and evening clouds and showers. Gradually building mid-
level heights may bring increasing stability by late in the weekend.


VFR conditions will prevail through tomorrow afternoon. However, a
weak cold front passing over Molokai and Oahu this afternoon may
generate ISOL MVFR conditions in showers as it continues its slow
march east southeastward. Clouds and showers along and behind the
front will favor the northern and windward sections of the islands
from Kauai to Maui. Meanwhile, convective buildups over interior
portions of Maui and the Big Island may become enhanced this evening
in response to the approaching front, and persist through most of
the night. Partial clearing is expected along the leeward coast of
the Big Island late tonight, otherwise vfr cloudiness will persist
all areas.

No AIRMETs are currently in effect or anticipated at this time.


The trade winds will continue to fill in behind the front as it
moves further down the island chain. The latest scatterometer from
10 am this morning showed 12-15 KT northeast winds throughout the
Kauai channel and between 15-20 KT northeast winds about 400 nm to
the west of Kauai. Unfortunately, the pass missed the western waters
surrounding Kauai. Winds are expected to stay within this range as
they increase behind the passing front. Therefore, no small craft
advisory looks to be needed.

The current northwest swell has peaked near 2 feet 12 seconds at the
Waimea buoy, 51201, this afternoon. These values are expected to
hold through the night before gradually lowering Tuesday.

The Lanai buoy, 51203, is picking up a - just above - 2 feet 13-14
second south swell, and the Barbers Point buoy, 51204, is showing a -
just above - 3 feet 13-14 second south swell. Farther south buoys,
51003 and 51002, suggest this will hold through the night. Some
lowering is expected during Tuesday, but another small southwest
swell is expected Tuesday night into Thursday.





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