Current Conditions
Temp3.5 C
RH41 %
WindNNE 14 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

745
FXHW60 PHFO 190150
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
350 PM HST Fri Sep 18 2020

.SYNOPSIS...
A high pressure ridge north of the island chain will keep moderate
to locally breezy trade winds in the forecast through Sunday.
Fairly stable conditions will keep shower activity brief for much
of this weekend in the isolated to scattered coverage range. Trade
wind speeds will decrease to more moderate levels through the
first half of next week. No significant changes to the rainfall
pattern for the next seven days.

&&

.DISCUSSION...
The big picture weather pattern remains unchanged with dry air
moving over the Hawaiian Islands in a stable atmosphere. The
subtropical ridge lingers north of the state will continue to
produce moderate to locally breezy trade winds through Sunday.
Trade winds will decrease through much of next week into a more
moderate range as the high pressure ridge north of the Hawaii
region weakens.

Shower activity will remain relatively low for the next few days.
Expect brief periods of isolated to scattered showers to continue
through Sunday due to a low subsidence inversion heights between
5000 and 7000 feet that will limit vertical cloud development.
In the longer range forecast for next week, model cross
sections continue to show an increase in the inversion heights by
Sunday. Typically higher thermal inversion heights will raise
cloud tops and increase the potential for periods of showers into
the forecast. However, current observational trends seem to favor
a drier forecast at least in the short term. Longer range trends
are showing a slight increase in shower activity through the
first half of next week. However, atmospheric forcing is weak
during this time period keeping our confidence in the higher
rainfall trends at a moderate level.

Dry fuels and low relative humidities will continue across the
leeward areas each afternoon through the weekend. However, wind
speeds are forecast to approach yet remain just below critical
fire weather thresholds through Sunday.

&&

.AVIATION...
Expanding coverage of cirrus is damping diurnal mixing just
enough to further suppress the already-limited coverage of cumulus
and isolated light showers for Oahu through Big Island. This trend
will continue for the remainder of the afternoon with nothing
more than very isolated light windward showers anticipated. An
uptick in coverage can be expected during the overnight hours,
but VFR is forecast to persist through the forecast period. Trades
will remain moderate out of the east.

No AIRMETS are in effect.

&&

.MARINE...
Strengthening high pressure to the northeast of the islands has
tightened the pressure gradient across the island chain,
supporting Small Craft Advisory (SCA) winds through the typically
windy channels around Maui County and waters south of the Big
Island. These winds are forecast to hold through Sunday
afternoon.

Surf will be on the rise along north and south facing shores this
weekend. Smaller-period, north-northwest swells will arrive today
from strong to near gale force winds behind a northern Pacific
cold front. This should provide a small bump along north and west
facing shores tonight through Saturday. Long-period, south-
southwest swells generated from last week's Tasman Sea storms will
drive surf heights above the summer average over the weekend, but
should stay below the advisory level of 8 feet. East shore surf
will increase a touch due to strengthened trade flow.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.


&&

$$

DISCUSSION...Bohlin
AVIATION...JVC
MARINE...TS

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