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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 241327
Area Forecast Discussion
National Weather Service Honolulu HI
327 AM HST Sat Jun 24 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 light to moderate trade winds across
the island chain early this morning. Infrared satellite imagery
shows partly to mostly cloudy skies in place across the State,
with cloud cover most prevalent over windward sections of Maui and
the Big Island, as well as just to the south of the islands over
the coastal waters. Radar imagery shows scattered showers moving
into windward areas, with rain free conditions elsewhere. Main
short term concern revolves around rain chances.
Today through Sunday,
High pressure will track slowly eastward well to the north of the
island chain through the weekend. Meanwhile, a mid-level (700 mb)
trough over the Big Island this morning, will track slowly
westward over the other islands today 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 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.
Light to moderate northeast to east trade winds will continue
today 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 over
mountains and along north through east slopes 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 weekend.
Fresh to strong trades are expected to return late Sunday night
into Monday and continue through the upcoming week as the gradient
tightens over the waters. 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
once again today, especially along south facing shores, where
surf will remain above normal. The greatest potential for coastal
flooding impacts will be during the mid to late afternoon hours,
when highest tides are expected. Visit tidesandcurrents.noaa.gov
for more specific information about forecast tides and water
levels in your area. Tides and surf along south facing shores 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