Current Conditions
Temp4.0 C
RH28 %
WindW 13 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

679
FXHW60 PHFO 190141
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
341 PM HST Fri Jun 18 2021

.SYNOPSIS...
Moderate trade winds are expected over the weekend, and into next
week with showers favoring windward and mountain areas. Some showers
will be heavy at times through Saturday, before normal trade wind
weather returns Sunday and continues into next week.

&&

.DISCUSSION...
High pressure located far northeast of the area is providing the
islands with moderate trade winds. An upper low centered about 150
miles north of Kauai is bringing some instability over the
western half of the state and radar bears this out showing some
enhanced afternoon showers over the southwest slopes of the
Garden Isle and over the Waianae Mountains on Oahu. Otherwise
over the islands, the weather is quite benign this afternoon with
mostly clear skies over leeward locations and partly cloudy skies
over windward areas with minimal showers activity. The upper low
is expected to meander eastward through Saturday and spread
limited instability over the state. The instability will allow for
embedded downpours within incoming trade wind showers along with
the possibility of a few thunderstorms over the Big Island slopes
Saturday afternoon. Some of the heavier showers will also reach
leeward locations.

By Sunday the upper low is expected to head north as a ridge
builds aloft. The ridge will cap our showers with a stabilizing
temperature inversion, and seasonal trade wind weather will resume
and continue into next week.

&&

.AVIATION...
No AIRMETs are in effect and none are expected this evening.

A high far northeast of the area will produce moderate east winds
over the main Hawaiian Islands. The easterly flow will carry
scattered clouds and isolated showers over east sections of the
islands. A low aloft north of Kauai is create some instability,
so heavy showers are possible, but the atmosphere is dry, so any
heavy showers will be very isolated.

&&

.MARINE...
A 1028 mb surface high pressure system lingers far northeast of
the region this afternoon with a surface ridge extending
southwest from the high center to an area roughly 600 nm north of
Kauai. This high pressure ridge will weaken as a cold front moves
into the Central Pacific basin. Moderate to fresh trade winds
will gradually weaken into the weekend. Another front will move
into the region north of the islands next week, pushing the
weakening surface ridge towards the islands causing another
decrease in coastal and offshore wind speed trends. No Small Craft
Advisories are expected over the next 5 days due to decreasing
wind speeds.

A series of long-period south swells will move into the region
through next week, with elevated surf forecast along south facing
shores. South shore surf heights will increase this weekend
peaking near the High Surf Advisory threshold from Saturday night
into Sunday. Surf heights along south facing shores will
gradually lower from Monday into the middle of next week. Surf
along north facing shores will remain small through the next five
days with just a small bump in surf heights late Sunday into
Monday as a small northwest swell moves into the region. A
weakening trade wind regime will keep surf heights small along
east facing shores through the middle of next week.

&&

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

&&

$$

DISCUSSION...Morrison
AVIATION...Donaldson
MARINE...Bohlin

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