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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 230129
Area Forecast Discussion
National Weather Service Honolulu HI
329 PM HST Sat Feb 22 2020
Southeasterly winds will persist for the remainder of the weekend,
with strengthening trade winds expected for the new work week. Low
rainfall totals are expected for Sunday, with trade wind showers
increasing throughout the week.
No major changes to the forecast or the forecast philosophy with
the afternoon package. The high to the northeast of the islands
has a ridge north of the islands. A front to the far northwest
will help to keep that ridge from building northward through the
remainder of the weekend, and as a result, southeasterly wind flow
No change in the models, so expecting the ridge to build north of
the islands with the new week, allowing trade winds to build back
in. The last couple models runs of the global models still show
winds continuing to increase as the week progresses, but perhaps
not quite as strong as the GFS showed a day ago. Have tapered back
the winds in the days 6 and 7 time period as a result.
Have also made some tweaks to the PoPs and associated fields
mainly in the days 3 to 7 time period to better follow a blend of
the models. As a general rule, expect an increase in showers in
comparison to the amount of showers this weekend. With the
returning trades, look for the showers to be focused over
windward and mauka areas. As the winds increase, some of the
showers will reach interior and leeward regions.
Winds are weak this afternoon and that will continue into Sunday.
Most areas are seeing southeast winds with some wind speeds low
enough to be allowing for a sea breeze. A lot of sites are at
10kts or below. Low clouds and isolated shower activity on the
windward slopes is possible but probably will be infrequent
through this forecast period with only passing MVFR conditions.
The remainder of the state will have VFR conditions.
A high remains far northeast of the area, with a ridge extending
from the high to about 450 nm north of Kauai. The pressure
gradient south of the ridge continues to produce locally strong
trade winds over the coastal waters. A Small Craft Advisory has
been extended through tonight for the windy coastal waters around
the Big Island and Maui. Wind directions have started to veer
slightly out of the southeast, so the areas where the winds are
strongest have shifted a bit. The Big Island Southeast Waters have
been dropped from the advisory and Big Island Windward waters
have been added.
Over the next couple of days a front will approach from the
northwest and a trough will develop ahead of the front. Winds will
weaken and veer out of the southeast on the east side of the
trough and back out of the northeast west of the trough. The front
will enter the northwest offshore waters Sunday night, then
dissipate. A new high moving east behind the front will bring a
return of trade winds across Hawaiian waters by Monday night.
A new moderate northwest swell building this evening will peak
tonight, then gradually lower Sunday through Monday. Surf from
this swell will remain well below the advisory threshold. A very
large northwest swell is expected to arrive Monday night. Surf
from that swell will peak well above the advisory level Tuesday,
and the surf may reach warning levels along north and west facing
shores. The swell will gradually subside through Thursday when a
new northwest swell will arrive. Moderate surf along east facing
shores will subside through early next week as the trade winds
weaken. Surf will remain small along south facing shores.
Small Craft Advisory until 6 AM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-
Big Island Leeward Waters.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office