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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 141752 AAA
Area Forecast Discussion...UPDATED
National Weather Service Honolulu HI
752 AM HST Mon Jun 14 2021
Minor adjustments in lowering cloud coverage and POPs for most
islands but particularly windward Big Island for this morning and
Moderate to breezy trade winds will continue this week. Low
clouds and showers will focus over windward areas, with showers
more active during nights and mornings. Daytime heating will
produce clouds and a few showers over the leeward slopes of the
Big Island during the afternoons and evenings.
No changes to the forecast in the near term with the morning
package. For the weekend, have started to trend the winds down
just a bit, with recent runs of both the ECMWF and GFS showing
weaker winds than what we had in the forecast.
Satellite shows the clouds near Maui County and Big Island last
evening have crept north to Oahu overnight, and have been moving
to the west. As such, skies over Maui County and the Big Island
area starting to clear out. Precipitable water (PW) values remain
below normal, and that is evident in the rainfall totals seen
statewide. The highest totals overnight were found at gages on the
Big Island, but even those were under half an inch in 6 hours.
High pressure remains north of the islands, and is expected to be
the driving force for trade winds through much of the week. Expect
moderate to breezy trade winds. A band of increased PW is about
220 miles northeast of the smaller islands, and is making its way
towards the islands. Expect this moisture to reach the islands
late today or tonight.
The high is expected to move eastward across the north central
Pacific as a complex low and front linger near the dateline. Look
for clouds and limited showers to remain focused over windward
areas, with some making it to leeward areas from time to time. An
upper low northwest of the islands is forecast to move toward the
state over the next few days as a separate frontal boundary
approaches from the north. This would lead to an increase in
shower coverage and intensity starting Tuesday night, initially
for Kauai and Oahu, and then spreading to Maui County over the
second half of the week. Trade winds will continue through this
time period, so showers will remain focused over windward and
As mentioned above, the trend in the global models is for a
weakening of the trade wind flow due to the high to the northeast
lifting northward through the weekend.
Moderate easterly trades will continue through Tuesday, with
clouds and showers favoring windward coasts and slopes. MVFR
conditions will be possible in and around showers moving through,
especially through the late night and early morning periods.
There are no AIRMETs currently in effect, however, AIRMET Sierra
can't be ruled out through the overnight and early morning periods
for mountain obscuration over windward areas.
High pressure north of the islands maintain moderate to fresh
trade winds over most of the coastal waters through next weekend.
Winds may reach Small Craft Advisory thresholds at times around
Maui and the Big Island.
Surf along south facing shores will remain small through
Wednesday, then rise, possibly reaching High Surf Advisory levels
next weekend. A short-period north swell will produce small surf
along north facing shores through Wednesday night. Surf along
north facing shores will be minimal through the rest of the week,
but a small northwest swell is possible early next week. Trade
winds upstream of the islands will produce only small and choppy
surf along east facing shores through the week.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office