761 
FXHW60 PHFO 230656
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
856 PM HST Mon Apr 22 2019

.SYNOPSIS... 
A trade wind weather pattern will continue through the work week,
with periods of clouds and showers expected to favor windward 
areas. Leeward areas will remain mostly dry. The trades will 
begin to decrease over the weekend, allowing for development of 
sea and land breezes. This will favor showers developing over 
leeward and interior sections of the islands during the daytime.

&&

.DISCUSSION...
A 1031 mb high far northeast of Hawaii is driving locally breezy 
trade winds across local waters this evening. Our airmass remains 
dry and stable, with weak upper ridging over the area. Afternoon 
soundings show strong inversions between 5000 to 6000 ft and PW 
between 0.9 and 1.1 inches. Satellite loop shows scattered to 
patchy broken low clouds over windward sections of the islands. 
Radar shows a few showers are associated with the low clouds. 
Leeward areas are mostly clear this evening. Kona cloud cover on 
the Big island is beginning to fade away as evening cooling sets 
in.

Models show trade winds will maintain speed through Wednesday, 
then weaken slightly towards the end of the work week. Low clouds 
and scattered showers will continue to push over the islands, 
focusing over windward and mauka areas. These showers will 
generally be light and occur mostly during the overnight and early
morning hours. Warm and mostly sunny conditions will continue for
leeward areas. 

Over the weekend, a weak surface trough will develop over the 
islands in response to an approaching upper trough. This will 
result in the trade winds weakening, veering east southeastly and 
allowing daytime sea breezes and nighttime land breezes to set up.
A weak front will also approach the islands from the northwest, 
but will likely fade before reaching Kauai. This weekend, expect 
an overall increase in clouds and showers, particularly across 
leeward and interior sections of the islands during the daytime. 

Models disagree on the strength of the forecast upper trough, with
GFS showing a weaker trough than depicted in ECMWF. There is potential
for locally heavy rainfall and/or thunderstorms on Sunday and 
Monday, but given the model differences that far out in the
forecast period, we will delay adding these to the grids. 

&&

.AVIATION...
High pressure center far northeast of Hawaii is very slowly
pushing to the northeast. It is pushing so slowly that it will
continue to provide the state with the stiff easterly/northeasterly
trades winds we have been experiencing. Therefore expect breezy to
sometimes windy conditions through tonight and especially through
the day Tuesday as the winds pick up speed during the day. AIRMET
Tango is in effect for low level turbulence below 6000ft downwind
of the mountains. There will be light, passing showers, especially
on the windward slopes tonight and Tuesday. So far there has not 
been enough moisture to warrant an AIRMET for mountain obscuration
and that should be the case through Tuesday as well.

&&

.MARINE...
Expect moderate to locally strong trades to continue into 
Thursday, with a decrease beginning on Friday and into the
weekend, as the ridge, currently north of the islands, gets nudged
eastward and replaced by a front that stalls north and west of the
islands. The Small Craft Advisory for the typical near-shore
waters around Maui and South of the Big Island, will be lowered 
around Wednesday night or Thursday.

Surf is expected to remain below advisory levels through the week
for all shores. There will be a series of small west-northwest to
north-northwest swells over the rest of the week. A moderate size
northwest swell is slated to arrive late Sunday afternoon, peak 
Sunday night, followed by a slow drop through Monday night. A
series of small south swells will maintain small surf along south
facing shores through the period. Surf along east facing shores 
will hold steady in the small to moderate range through Thursday 
due to the breezy to locally strong trades, then drop into the
weekend as the trade winds become light.

&&

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

&&

$$

DISCUSSION...Powell
AVIATION...Chevalier
MARINE...Lau