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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 081352

Area Forecast Discussion
National Weather Service Honolulu HI
352 AM HST Fri Dec 8 2023

Mostly dry weather will persist for the next couple of days, but a
weak front may bring some showers to Kauai late tonight. Light and
variable winds will continue into Saturday, with moderate to locally
breezy trade winds developing later in the weekend. Strong northeast
trade winds may develop on Tuesday, bringing an increase in windward
showers through Wednesday.


A front approaching from the NW has significantly loosened the low-
level pressure gradient as the parent lows have forced our trade-
wind-supporting high far NE of the area. With a surface ridge just
NE of the islands, light and variable winds prevail over land, with
low-level flow favoring a WSW direction over Kauai and Oahu, and ESE
direction near Maui and the Big Island. A narrow and weak cloud band
extending N from Molokai marks where this flow is weakly convergent,
producing just a few showers. Otherwise a mostly dry regime
persists, with radar showing a few small showers over near shore
waters, and over windward and SE portions of Maui and the Big
Island. Light showers that had been quite persistent along the Hana
coastline have eased this morning. Land breezes elsewhere have kept
any showers from moving ashore overnight.

Afternoon sea breezes will likely drive the formation of a few
interior clouds today, with just a few showers expected. Little
overall change is expected for most areas tonight as the slowing and
weakening front draws closer to Kauai, where it may bring a modest
increase in clouds and showers. As the front dissipates near Kauai
on Saturday, a weak high passing N of the area will support a mostly
dry, moderate to locally breezy trade wind flow into Monday.

A new high building far NW of the area Tuesday may lead to increased
NE trade winds, and may also push increased low-level moisture (from
the remnants of a front) over windward areas. Forecast models have
yet to agree on a unified solution as to the timing and extent of
the moisture increase Trade wind flow appears to be the most likely
outcome for the second half of next week.


Surface ridging ahead of an approaching cold front is keeping
background winds light across the islands early this morning, though
the light winds are favoring an east-southeasterly direction across
the eastern end of the state. This is allowing some isolated showers
to move into east and southeast sections of the Big Island, but
prevailing land breezes are keeping skies mostly cloud- and shower-
free across the remaining islands.

With the weak winds remaining in place today, expect land breezes to
linger through mid-morning before sea breezes begin to develop
across the islands. Interior cloud cover will therefore increase
during the afternoon, but moisture will be limited so showers will
be isolated at best. VFR flight conditions are expected to prevail
at most locations throughout the forecast period. Looking ahead, as
the front approaches Kauai Friday night into early Saturday, an
increase in showers and clouds can be expected over the western end
of the state.

There are currently no AIRMETs in effect. However, model guidance
shows that upper level turbulence will increase across the islands
from west to east later today and tonight as an upper trough moves
through. AIRMET Tango for moderate upper level turbulence is likely
to be needed by late this afternoon or early evening.


A weakening cold front approaching from the northwest today will
disrupt the trade wind flow and allow light and variable winds to
dominate across the state through tonight. High pressure will
briefly rebuild north-northeast of the area Saturday, allowing
moderate to locally fresh easterly trades to return across the
coastal waters into Monday, strongest over the eastern half of the
island chain. Winds are forecast to increase out of the northeast
beginning Monday afternoon/evening and spread eastward as the front
moves through the western portion of the coastal waters through mid-

A small, medium-period north swell will maintain elevated surf
levels along north facing shores this morning. A moderate, medium-
period northwest swell (320 deg) is slated to arrive this afternoon
and build down the island chain through the evening. This swell will
increase surf along north and west facing shores, likely reaching
the High Surf Advisory threshold as it peaks late tonight into early
Saturday morning. Surf will lower slightly as we head into the new
week, but remain elevated due to another northerly pulse set to
arrive Sunday night. A larger, moderate-period northwest swell (320
deg) is forecast to move through the local waters Tuesday through
the middle of next week, peaking well above advisory level, then
becoming more northerly (340-350 deg) as it slowly decreases heading
into Thursday.

Surf along east facing shores will continue to smooth out as winds
become light today. Beginning Sunday, rough and choppy surf will
return to east facing beaches as easterly trades return. Along south
facing shores, only small background swell energy is expected
through the forecast period.






Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office