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RH8 %
WindWSW 13 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

362
FXHW60 PHFO 260627
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
827 PM HST Thu Apr 25 2019

.SYNOPSIS...
A cold frontal system passing through the Central Pacific will
weaken the high pressure ridge north of the islands. Wind speeds
will weaken and veer towards the southeasterly direction tomorrow.
Shower activity will increase this weekend across the state with
locally heavy showers and thunderstorms possible on Sunday and
Monday. Trade winds return on Tuesday with more stable weather
conditions as a high pressure ridge builds back in north of the
state.

&&

.DISCUSSION...
The high pressure ridge north of the islands will weaken rapidly
this evening as a cold frontal system moves across the Central
Pacific basin. Wind speeds will weaken tomorrow and veer towards a
more southeasterly direction. Elevated showers may develop along
the east to southeast slopes of both Maui and the Big Island from
Friday afternoon to Friday evening. Isolated to scattered windward
and mountain showers will linger over the rest of the state.

The weather pattern gradually changes this weekend with light
winds allowing land and sea breezes to develop over all islands
ahead of a cold front that will likely stall northwest of the
island chain. A broad upper level trough pattern will lead to more
unsettled weather conditions from Saturday into Sunday with clouds
and scattered showers developing over island interior sections by
afternoon. On Sunday night a stronger short wave trough aloft
moves into the state from the northwest direction. This trough
will create unstable conditions with deeper convective showers,
leading to locally heavy rainfall and thunderstorm activity. The
western islands will feel the impacts of this trough on Sunday
night with deeper showers spreading southeastward down the island
chain to the rest of the state on Monday.

By next week Tuesday we return to a moderate trade wind weather
pattern as the low pressure system drifts eastward and another
high pressure system moves into the Central Pacific. Some clouds
and showers associated with the stalled cold front may drift into
Kauai and Oahu on the trades trending toward the windward and
mountain sections of each island. Trade wind weather will continue
through the first half of next week.

&&

.AVIATION...
Trade winds will be in the light to moderate range through tonight
as a high pressure ridge remains north of the state. However,
with a front approaching the area from the northwest, winds will
begin to veer to the southeast Friday.

VFR will prevail, with only isolated areas of showers and lower
ceilings in windward and mauka sections over the individual isles.

No AIRMETs are currently in effect.

&&

.MARINE...
Light to moderate trades will continue through Friday before
becoming light and variable over the weekend. An approaching front
from the west will nudge the ridge north of the islands away, and
replace it with light and variable winds, that will last through
early next week. Under this light wind regime, expect daytime sea
breeze along the coast and nighttime land breeze.

Expect an uptick in showers as well area-wide, especially during
the afternoons and evenings. Further more, an upper level trough
will bring a slight chance of thunderstorms over the surrounding
waters for Sunday through Monday.

Small but steady surf will continue along north facing shores
through the weekend due to a couple of recent systems passing north
of the islands. The current north swell will begin to veer north-
northeast on Friday and will hold through the weekend. A moderate
size northwest swell is expected to build through the day Sunday
and peak Sunday night into Monday and gradually ease through
midweek. Surf will remain well below advisory levels.

For the south facing shores, a similar trend will continue during
the first half of the period, with a series of long- period pulses,
spaced a couple of days apart. For the long range, more small
long- period swells are expected through next weekend.

As the trade winds become even lighter, so will the locally
generated trade wind swell. Therefore, expect small surf along the
east facing shores over the weekend and into early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Bohlin
AVIATION...JT
MARINE...Lau

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