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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 170200
Area Forecast Discussion
National Weather Service Honolulu HI
400 PM HST Mon Oct 16 2017
High pressure north of Hawaii will keep a windy trade wind
pattern in place through much of the upcoming work week, with the
trades trending down slightly Friday and weakening further over
the weekend. Clouds and showers will favor windward and mauka
areas through the period, but showers will reach leeward areas
from time to time as well due to the strength of the trades.
A 1029 mb surface high centered around 925 miles north of Honolulu,
is driving windy trades across the island chain. Visible satellite
imagery shows partly to mostly cloudy skies, with cloud cover
most prevalent over windward and mauka sections. Scattered showers
continue to focus over windward areas, occasionally passing to
leeward sides of the smaller islands due to the strong trades.
High pressure north of the state will slowly move southwest over
the next couple of days, with a re-enforcing high building in
behind it midweek. The high will then move southeast and weaken
Friday, and especially over the weekend as a cold front
approaches from the northwest. As a result, a tight pressure
gradient will remain in place over Hawaii, and will persist the
windy trades through Thursday. A Wind Advisory remains in effect
for the entire state with the exception of the Haleakala and Big
Island summits through 10 pm this evening. The Wind Advisory will
likely be need to be extended for some areas of the state for
Tuesday, and possibly on Wednesday and Thursday. Trades will
taper off on Friday, and then weaken further over the weekend.
As for sensible weather details, fairly typical trade wind weather
is expected continue through the next several days, with clouds
and showers favoring windward and mauka areas. Showers coverage
will be greatest at night, and then tapering off during the
The latest GFS solution indicates that some tropical moisture may
try to lift northward into the islands by Sunday as winds shift
southeast ahead of an approaching cold front. The ECMWF solution
delays the moisture arrival until Monday. Will keep the forecast
featuring typical trade wind weather through next weekend and
await better model agreement before deviating away from climatology.
Strong and gusty NE trade winds will continue through most of the
week. AIRMET TANGO for low level turbulence is posted across the
Scattered showers will continue to move over with the
trades. Most clouds and showers will focus along the windward and
mauka areas; the strong trade winds will carry a few showers to
leeward areas. Periods of MVFR CIGS/VIS can be expected in
passing showers. Otherwise, VFR conditions will prevail.
Very strong and gusty trade winds will continue through much of
this week due to a nearly-stationary, strong surface high N of
the main Hawaiian Islands. This high will be replaced by another
strong on Wednesday night, continuing the windy conditions for an
additional day or so. Gale warnings are posted for the Pailolo
and Alenuihaha channels Thursday afternoon, while a Small Craft
Advisory remains in effect for the remaining Hawaiian waters
through the same time. Trades should begin on Friday as the high
starts to weaken and move off to the east.
The strong to gale-force trade winds are also causing very rough,
choppy, and dangerous seas around the islands. Surf is also
elevated along E facing shores of all islands, with a high surf
advisory in effect through Wednesday afternoon. This advisory
will likely be extended toward midweek.
A long-period S swell will peak this evening through Tuesday
morning around 4 feet. The High Surf Advisory for the S facing
shores of all islands has been extended through Tuesday due to the
lingering swell. The next S swell will be a smaller and is slated
for the upcoming weekend.
The current NNW swell is on its way down with a shorter period.
The next NNW swell is slated to arrive Thursday night, building to
a peak of around 6 feet early Friday with a long period of 16 to
19 seconds. Expect moderate size surf from this swell, but
remaining below advisory level. A somewhat larger NW swell is due
in Sunday night and Monday of next week, with the surf potentially
approaching high surf advisory levels along the N and W facing
The Oahu Surf Discussion (SRDHFO) has detailed information regarding
the swell sources.
Strong trade winds coupled with a drier airmass pushing over the state
will allow minimum relative humidity to drop into the 40 to 45 percent
range during the next few afternoon. These conditions create
potential for a fire to ignite easier than usual and to spread
quickly if they do. The windy and relatively dry conditions will
continue through the end of the work week before the trade winds
weaken. The Keetch- Byram Drought Index, or KBDI, is at 572 today
(and would need to be at 600 for Red Flag Warning criteria).
Keep in mind that we will be close to these conditions each
Wind Advisory until 10 PM HST tonight for all portions of the
state except for the Big Island summits and Haleakala summit.
High Surf Advisory until 6 PM HST Tuesday for south facing shores
of Niihau, Kauai, Oahu, Molokai, Lanai, Kahoolawe and the Big
High Surf Advisory until 6 PM HST Wednesday for east facing
shores of Kauai, Oahu, Molokai, Maui and the Big Island.
Gale Warning until 6 AM HST Thursday for Pailolo Channel and
Small Craft Advisory until 6 AM HST Thursday for all remaining
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office