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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 240644

Area Forecast Discussion
National Weather Service Honolulu HI
844 PM HST Fri Jun 23 2017

A mid level trough will pass over the islands this weekend,
weakening the trade winds and increasing showers across the area.
The mid-level trough will shift west of the state by early next
week, with high pressure then building back northeast of the
islands. This will result in a drier and more stable trade wind
regime, with the trades increasing into the breezy to locally
windy range through much of next week.


Currently at the surface, a 1034 mb high centered 1600 miles
north of Honolulu is driving moderate trade winds across the
island chain this evening. Infrared satellite imagery shows partly
to mostly cloudy skies in place across the state, with cloud
cover most prevalent over windward areas, as well as leeward
sections of the Big Island. Radar imagery shows scattered showers
moving into mainly windward areas, with some lingering daytime
shower activity over leeward sections of the Big Island. Main
short term concern revolves around rain chances.

Tonight through Sunday,
High pressure to the north of the State will track slowly eastward
well to the north of the island chain through the weekend.
Meanwhile, a mid-level (700 mb) trough just to the east of the Big
Island this evening, will track slowly westward through the
islands Saturday through Sunday. A weak surface reflection in the
form of weak surface troughing, will weaken the trade wind flow
across the islands, resulting in localized sea breezes in the more
sheltered areas each afternoon. Showers will continue to favor
windward and mauka areas through the weekend, but there will
likely be some afternoon shower development in leeward areas due
to the weakened trade wind pattern, with these showers lingering
into the evening hours each day. A few of the showers could be a
bit heavier as a result of the mid-level trough moving overhead,
but no significant flooding issues are anticipated.

Sunday night through next Friday,
The mid-level trough will exit to the west of the state, while
surface high pressure builds to the northeast of the island chain.
This will increase the pressure gradient across the islands,
resulting in strengthening trade winds Sunday night and Monday,
with breezy to locally windy conditions expected Tuesday through
the end of the upcoming work week. In addition to the
strengthening trades, with the exit of the mid-level trough to the
west of the islands, a drier more stable airmass will move into
the area. Precipitable water values will drop into the 1.0 to 1.2
inch range, below normal for this time of year, and this will
result in a drier than normal trade wind shower pattern. Showers
will continue to favor windward and mauka areas, with a stray
shower reaching leeward areas from time to time due to the
strengthening trades. Rainfall amounts are expected to remain
light through the period.


Breezy northeast to east trade winds are forecast on
Saturday with a trend towards late morning to afternoon onshore
sea breezes and cloud build ups along western slopes of all
islands. Tempo showers and ceilings with isolated MVFR possible
mainly along north through east slopes and coasts of all islands

No AIRMET's in effect with none expected.


Moderate to fresh trade winds associated with 1034 mb high
pressure far north of the state will continue through the
overnight hours, then weaken Saturday and Sunday as the gradient
relaxes. There is a slight chance for some coastal areas to
experience sea breeze conditions through the late morning and
afternoon periods over the weekend, however, confidence in this
potential remains low at this time. Fresh to strong trades are
expected to return through the day Monday and continue through the
remainder of the week. Small craft conditions will become likely
through this period over the typically windier channel waters,
Maalaea Bay and south of the Big Island.

Coastal flooding associated with King tides will be a possibility
going into the weekend, especially along south facing shores,
where surf will remain above normal through Saturday. The
greatest potential for coastal flooding impacts will be during the
mid to late afternoon hours Saturday, when highest tides are
expected. Visit for more specific
information about forecast tides and water levels in your area.
Tides and surf will lower Sunday into the upcoming week.

Surf along east facing shores will build early next week due to a
combination of a moderate northeast swell associated with a batch
of gales off the west coast and increasing trade winds locally and
east of the state. There still remains some uncertainty of the
size of this swell and whether or not a high surf advisory will be
needed for east facing shores next week. Regardless, rough surf
seems likely for east facing shores next week.

For more details on the surf, please refer to the Oahu
Collaborative Surf Forecast (SRDHFO).






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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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