Current Conditions
Temp9.4 C
RH14 %
WindNE 0 mph
RoadOpen (4x4)
Menu of Text Products for the Hawaiian Islands and the Tropical Pacific/Atlantic Oceans:
Narrow the Menu List
Select Time Limit: 12 hours | 24 hours | 48 hours | 72 hours | No time limit
Select Product Type: All | Routine Bulletins/FCSTS | Warnings/Watches/Advisories | HAWN Weather | Tropical | Marine | Aviation | Daily Obs | Special
Hawaiian Islands Synoptic Discussion and Guidance

192
FXHW60 PHFO 231332
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
330 AM HST Fri Jun 23 2017

.SYNOPSIS...
Moderate trade winds today will trend lighter over the weekend, but
will continue to deliver passing clouds and showers to windward
areas, mainly during nights and mornings. The lighter winds will
likely allow sea breezes to drive the formation of afternoon and
evening clouds and a few showers over leeward areas of all islands,
and a weak disturbance aloft may allow a few briefly heavy showers
to develop, especially on Sunday. Breezy trade winds are expected to
develop early next week.

&&

.DISCUSSION...
A somewhat static pattern to the N of the area, with slow-moving
high pressure cells centered far to the NNW and NNE, with a low and
associated stalled front separating the two. The low-level gradient
S of these highs is supporting trade wind flow over the islands,
with speeds ranging from light in sheltered leeward locations to
breezy in the more exposed areas. Overnight soundings continue to
indicate that the island atmosphere remains capped at a height near
8 kft, which is sufficiently low to prevent significant rainfall,
but also sufficiently high to allow efficient warm rain processes to
produce light to moderate showers, especially given that PWAT is
around 1.2". Water vapor imagery shows that a low aloft about 1200
miles NE of the islands has weakened to a trough while a weak trough
aloft is approaching from the distant NW.

Little significant change to the overall weather pattern is expected
today, with moderate trade winds delivering passing clouds that will
fuel a few showers, mainly over windward areas this morning,
although showers may linger into the afternoon over windward Maui
and Big Island. A trend toward weaker trade winds is anticipated
Saturday and Sunday as a weakness in the low-level gradient, and
potentially a weak low-level trough, moves over the islands from the
E. At the same time, a subtle increase in low-level moisture is
expected to arrive on the trade flow.

The trough aloft approaching from the NW will act to slowly and
steadily cool mid-level temperatures as it sharpens near Kauai later
this weekend into next week. This feature, combined with the arrival
of increased moisture, is expected to maintain passing showers over
windward areas. In addition, the light winds will likely allow
afternoon sea breezes to drive the development of clouds and showers
over leeward and interior areas, with the trough aloft potentially
allowing a few showers to become briefly heavy. Latest guidance
indicates that greatest instability, although still modest, will be
over Kauai and Oahu, and centered on Sunday. Light winds and slower
shower movement means there will be a chance for higher localized
rain totals where any showers do develop. The combination of light
winds, the extreme sun angle, and dew points near 70F will likely
make for sticky conditions over the weekend. Although the developing
trough aloft may bring periods of high cloudiness later this weekend
and early next week, confidence in their thickness and location has
precluded their inclusion in the forecast at this time.

Early next week, the high to the NNW will move E, and models agree
that breezy ENE trades will develop, delivering a few showers to
windward areas. A ridge aloft is expected to build over the area
from the NW as the trough aloft dissipates and moves SW.

&&

.AVIATION...
Light to locally moderate trade winds will persist through the
period. Ragged clouds and scattered showers will continue to favor
windward and mountain areas. Brief MVFR conditions possible in
passing showers, especially at night. Otherwise VFR conditions will
prevail all areas. No AIRMETs in effect or anticipated at this time.

&&

.MARINE...
A ridge of high pressure north of the islands will keep moderate to
occasionally breezy trade winds in place through the weekend, but
winds and seas are expected to remain below Small Craft Advisory
(SCA) levels. The trades are expected to strengthen early next week
as high pressure builds northeast of the islands, and SCA for winds
may be needed for the typically windy waters at that time.

A new reinforcing SSW swell will peak near or just below advisory
levels today. Surf along south facing shores will remain above
average Saturday and Sunday, and into early next week, but remain
below advisory levels.

In addition to the new southerly swell, tides have been running
about a half a foot above predicted levels. These elevated tide
levels will increase the risk for minor coastal flooding when
combined with the above average south swell. For the next few
afternoons, the predicted high tides are around 2.5 feet MLLW, which
does not include the extra 1/2 foot mentioned above. See the latest
Special Weather Statement (SPSHFO) for additional details on the
elevated tide levels and potential impacts.

Small trade wind and SE swells will continue into the weekend. In
the longer range, models indicate a northeast swell developing for
the beginning of next week. A High Surf Advisory may eventually be
needed for east facing shores if the swell comes in bigger than
anticipated.

For more details on the surf, please refer to the Oahu Collaborative
Surf Forecast (SRDHFO) prepared by Pat Caldwell under WMO header
FXHW52 PHFO.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

Discussion...Birchard
Aviation...Bedal
Marine...Kinel

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office