Drought in Hawaii, July 21 to 31, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
828 PM HST Mon Jul 20 2020

.SYNOPSIS...
Breezy trade winds will continue through the overnight hours with
showers focused mainly along windward and mountain slopes of each
island. Wind speeds will decrease on Tuesday and Wednesday as an
upper level low drifts north of the island chain disrupting the
trade winds and allowing local scale land and sea breezes to
develop especially over leeward areas. Shower activity will trend
higher from Wednesday onward and moderate to breezy trade winds
return from Thursday into the weekend.

&&

.DISCUSSION...
The satellite picture this evening shows an upper level low
northeast of the Big Island drifting towards the islands. Two
Tropical Cyclones (TC) are brewing in the Eastern Pacific basin.
The northern TC 07E appears to be weakening in a stable stratus
cloud environment. The stronger TC 08E is located further south in
more unstable tropical air and continues to develop and drift
westward towards the Central Pacific basin. Otherwise extensive
cloud bands are upstream of the islands and will support
overnight showers focused along the windward sides of each island.

The upper low northeast of the islands will drift westward for
the next few days, weakening the trade winds, and producing a
local scale land sea breeze pattern on Tuesday and Wednesday.
Enough instability from the upper low will keep above normal
shower trends in the forecast on Wednesday. As the upper low
drifts away from the islands on Thursday trade winds will increase
across the state. Expect moderate to breezy trade winds from
Thursday on into the upcoming weekend, with showers focused over
windward and mountain areas favoring the overnight and early
morning time periods.

Global model solutions look good through Friday. The model
guidance for this weekend continue to diverge a bit as TC 08E
approaches the state from the east-southeast. Our confidence in
the long range weekend forecast remains low side due to these
model inconsistencies. Stay tuned for updates to this long range
forecast as changes are likely.

&&

.AVIATION...
A trough of low pressure will approach from the east tonight and
move over the islands on Tuesday, easing the trade winds. Showers
will favor windward slopes and coasts tonight and early Tuesday,
and AIRMET Sierra may be needed for mountain obscuration in some
of these areas later tonight. Showers will favor interior and
leeward areas Tuesday afternoon, and AIRMET Sierra may be needed
for some of these areas due to mountain obscuration as well.

AIRMET TANGO remains in effect for moderate low level turbulence
over and downwind of the terrain of all islands. Conditions
should improve later this evening.

&&

.MARINE...
Moderate to locally strong trade winds will persist through
tonight, then trend down Tuesday through midweek as a broad trough
moves through. Strongest winds are expected in the Alenuihaha
Channel tonight, where a Small Craft Advisory remains in place.
Seas will respond and trend down over the next few days. A return
of fresh to strong trade winds is expected Thursday through Friday
as this trough shifts west of the area.

Although forecast uncertainty remains high through the upcoming
weekend due to significant model differences, interests are
encouraged to monitor the latest forecasts from the National
Hurricane Center over the coming days as newly formed Tropical
Storm Douglas in the eastern Pacific continues westward. Douglas
is forecast to enter the central Pacific basin Friday (around 900
nautical miles east-southeast of Hilo), then approach the Big
Island waters over the weekend. Confidence in the details will
rise over the next few days as conditions evolve.

Surf along east facing shores will remain choppy due to breezy
trades into Tuesday. Although the winds are forecast to ease
through the midweek time frame, moderate surf should hold due to
a new 9-10 sec period northeast swell expected to arrive from a
recent area of strong- to gale-force winds off the California
coast. This should hold into Thursday, then lower into Friday.
Although confidence remains low as previously mentioned, a rising
trend will become a possibility over the weekend for the eastern
end of the state as Douglas approaches the region.

A small, long-period south-southwest swell will continue to fade
into Tuesday, leaving mainly a mix of small background energy
moving through. A similar sized southerly swell will be possible
come Wednesday, which will support an upward trend into the second
half of the week.

Surf along north facing shores will remain around the summertime
average each day - exception being at the typical locations
exposed to trade wind/northeast swell energy.

The combination of seasonally high astronomical tides and
abnormally high sea levels will likely produce nuisance coastal
flooding during the next several days. This will be particularly
noticeable during the afternoons during the highest tide of the
day. Low lying infrastructure will be susceptible to this
flooding. Visit tidesandcurrents.noaa.gov for information about
forecast astronomical tides in your area.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Tuesday for Alenuihaha
Channel.

&&

DISCUSSION...Bohlin
AVIATION...Jelsema
MARINE...Gibbs