Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 210648

Area Forecast Discussion
National Weather Service Honolulu HI
848 PM HST Sun Oct 20 2019

Light winds are expected through tonight as high pressure lingers
far to our northeast. Showers will continue to favor windward and
mauka areas. Moderate trades are expected to return on Monday and
linger through Thursday with passing showers focused over windward
and mauka areas, especially during the night and early morning
hours. Trade winds will become lighter as we head into next
weekend due to a front developing to our north.


Have decreased PoPs overnight for the western end of the state,
based on the latest satellite and radar data. Satellite derived
precipitable (PW) continues to show the highest values to the
southwest outside the coastal waters, and the values over Kauai
and Oahu and surrounding waters should be on the decline

The general forecast philosophy remains the same for the forecast
period. Satellite derived PW shows some increased moisture east of
the Big Island that could be moving in there by tomorrow
afternoon. PW values are around 1.6 inches which is near normal
for October, so just looking for an increase in some of the trade
wind showers mostly over the windward side of the island.

The front to the far north is weakening as it continues to move to
the east tonight. By Monday morning, we expect the ridge to the
north to lift northward, which will allow winds to become more
easterly across the state. This will also allow wind speeds to
rebound back to more moderate levels into the middle of the week.
Expect passing trade showers through Thursday focused over the
typical windward and mauka areas.

Heading into the next weekend, another front to the north of the
islands will once again turn the winds to the southeast. The
latest global model runs are showing an uptick in PW coming in
over the islands from the southeast during this time. Will have to
watch future model runs to see how much PW will make it into the
islands and when, to determine any such impact.


Trade winds will re-strengthen as we head into Monday, which will
focus most of the clouds and shower activity on the windward side
of the islands for the next few days. Brief MVFR conditions are
possible in passing showers, but VFR conditions are expected to
prevail, with no AIRMETs expected through Monday.


Since the most current winds remain at borderline Small Craft
Advisory (SCA) speeds, the SCA continues through Monday

A front will stall well north of the islands and dissipate
Monday, which will result in the nearby ridge moving north and
strengthening. This will boost winds slightly across the area and
will likely lead to an expansion of the SCA to include other
typically windy zones by Tuesday. Another front approaching late
in the week may once again lead to diminishing winds.

Small background northwest swells will persist over the next
several days along north facing shores. Further out, the latest
model guidance is indicating surf rising late Wednesday through
Thursday and peaking Friday along north facing shores. There are
still some uncertainties with the swell heights as the swell
makes it to local shores. However, with the typical low bias of
these models, the isles may see surf heights near High Surf
Advisory levels along north and west facing shores later this

Trade winds will push short-period wind waves onto east facing
shores for at least the next couple of days, trending down later
in the week. Surf along south facing shores will remain small
through the week with mainly background swells out of the SW, S,
and SE.


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



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