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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 280150
Area Forecast Discussion
National Weather Service Honolulu HI
400 PM HST MON JUN 27 2016
High pressure north of the area will maintain trade winds through
the holiday weekend. Ridging aloft will keep the atmosphere dry and
stable through tomorrow, so rainfall will be light and confined to
mainly windward areas. A low aloft will move south over the area
Wednesday and make the atmosphere unstable, so showers may become
more active through Thursday. On Friday the atmosphere will become
more stable and much drier and rainfall will become sparse. A strong
high building northeast of the area will bring windy weather over
the holiday weekend.
A strong 1030MB high 930 miles north northwest of Kauai at 36N 166W
will move south slowly and weaken over the next few days. This high
will keep trade winds breezy through tonight. A ridge aloft
southwest of the area will keep the atmosphere fairly stable and dry
through tomorrow, so rainfall should remain rather light.
The global models are in good agreement showing a trough digging
southeast toward the area tomorrow. A low aloft is forecast to form
north of Kauai tomorrow night, then move southwest slowly through
Thursday night. The low will bring colder air aloft, resulting in
the airmass over the islands becoming more unstable. An area of low
level moisture about 350 miles east of the islands will be moving
over the islands by Wednesday so the atmosphere will also be getting
more moist. Showers will likely become more active Wednesday and
Thursday and thunderstorms may be possible.
Starting Thursday night, the low aloft will move off to the west and
ridging aloft will build over the islands from the southeast. As
that happens, the atmosphere over the islands will turn drier and
more stable, and showers will become less active. A strong surface
high will build far northeast of the state by next weekend. Trade
winds will strengthen and it may be quite windy through the
Independence Day weekend.
VFR will prevail, but brief MVFR ceilings and visibilities will be
possible in passing SHRA over windward areas, with PHTO the most
likely TAF site to be impacted. AIRMET SIERRA for MTN OBSC may need
to be issued at times.
AIRMET TANGO is in effect for mechanical turbulence immediately
south through west of mountains on all islands below 8000 feet and
the AIRMET is likely to stay up through at least this evening.
A strong high far northwest of the area will produce strong trade
winds in the windy zones around the Big Island and Maui tonight, so
a Small Craft Advisory remains in effect for those areas. We expect
to drop the advisory tomorrow. A new high will build northeast of
the area during the second half of the week. That high is forecast
to become unusually strong, and could push the trade winds up near
gale force in the windier areas over the holiday weekend.
Surf will remain below High Surf Advisory (HSA) levels along all
shores for at least the next few days. The current south swell will
persist through tomorrow. After that, smaller than normal surf is
expected along south facing shores through the holiday weekend.
Fairly small but rough surf along east facing shores will subside
tomorrow as the trade winds weaken. Surf will rebuild along the east
facing shores over the weekend as the trades strengthen again.
Starting Thursday night, the atmosphere over the islands will become
quite stable and very dry air will spread over the area from the
east. Wind speeds will increase significantly by the weekend as a
strong high builds north of the islands. The low humidity and strong
winds will boost the fire danger over the weekend.
Small Craft advisory until 600 AM for the Pailolo and Alenuihaha
Channels, Maalaea Bay and waters south of the Big Island.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office