Area Forecast Discussion
Issued by NWS Honolulu, HI
FXHW60 PHFO 310641
Area Forecast Discussion
National Weather Service Honolulu HI
841 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
The SKY and POP grids for northern Big Island and the adjacent
waters have been adjusted higher for the overnight hours as the
front is about to enter the Alenuihaha Channel, which is a tad
faster than forecast. A line of pre-frontal showers have formed
extending from windward Kohala to the waters just off Honakaa.
The rest of the forecast package looks good into Tuesday with
somewhat of a wet trade pattern for most of the islands.
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.
With a weak front in the vicinity, TEMPO MVFR is likely over the
isles from Kauai to Maui; especially in northern, windward, and
mauka sections; as broken lower cloudiness and showers move
toward the south and southwest. However, VFR will predominate
No AIRMETs are currently in effect.
The trade winds will continue to fill in behind the front while
a modestly strong 1025 mb surface high moves to a position some
700 miles north of Kauai by Tuesday afternoon. The trades will be
strengthening gradually to moderate speeds during the overnight
hours and Tuesday. We will be monitoring the trades closely if it
will reach small craft advisory, SCA, criteria. There is a slight
hint of this occurring with waters around Kauai on Tuesday. If
an SCA is issued, the duration will be short live, about 24 hours
as the High starts to weaken on Wednesday.
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.
For the south swell, the Lanai buoy is still showing a solid 2.6
ft with a 14 seconds this past hour. So is Barbers Pt., at 3.6 ft
at 13 secs. Some lowering is expected Tuesday, but another small
southwest swell is expected Tuesday night into Thursday.