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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 231942
Area Forecast Discussion
National Weather Service Honolulu HI
942 AM HST Tue Jul 23 2019
A high pressure ridge north of the Hawaiian Islands will continue
to produce easterly trade wind weather across the region through
the middle of next week. Two low pressure systems just west of
Kauai will produce decreasing layers of mid and high level clouds
across Kauai today. Otherwise drier and more stable trends are in
the forecast through the weekend.
Satellite imagery this morning shows an upper level low roughly
600 miles northwest of Kauai and a low level trough 400 miles
southwest of the island. Instability and lift associated with
these two systems are producing a decreasing layer of middle and
high level clouds across Kauai this morning. Radar imagery shows
some convective showers just south and west of Kauai and Niihau,
these showers will diminish in coverage through the morning hours.
Elsewhere fairly stable clouds are moving into the islands from
the east with the trade winds.
A high pressure ridge north to northeast of the state will keep
moderate to breezy trade winds in the forecast into the middle of
next week. An upper level low located northwest of Kauai and a low
level trough southwest of the island continues to produce mostly
elevated middle and high level clouds from Kauai to Molokai this
morning. These low pressure systems will slowly drift westward away
from the islands over the next few days with upper level cloud
cover diminishing later tonight. An upper level ridge will then build
in across the state from the east producing more stable conditions
with a stronger subsidence inversion limiting shower activity.
Weather conditions into the upcoming weekend are similar in a
persistent easterly trade wind weather regime. Expect isolated to
scattered showers mainly over windward and mountain areas of each
island favoring the overnight to early morning hours. Little to no
rain is forecast over leeward areas through Sunday.
Long range global weather models are hinting at another upper
level low developing just to the northeast of the Hawaiian Islands
by Monday morning. Additional showers are possibly in this
scenario for the first half of next week, especially along
windward and mountain slopes. However, our confidence in enhanced
shower activity over Hawaii this far out remains poor due to
large uncertainties associated with the strength and position of
this developing system five days into the future. Stay tuned for
updates to next weeks precipitation forecast as the time period
Strong high pressure far to the northeast will maintain locally
strong east to northeast winds over the area. AIRMET TANGO is in
effect for moderate turbulence to the lee of the mountains.
Conditions are expected to persist through at least early evening,
but may abate across Kauai and Oahu later this evening.
The surface low to the southwest of the state will continue to
track slowly northwest. Thick layered clouds still cover Kauai
county, but conditions area expected to gradually improve today
from the east. Isolated thunderstorms just outside Hawaii coastal
waters are expected to remain south and west of the AOR.
Otherwise, low topped stratocumulus embedded in the trade wind
flow will continue to impact mainly east and northeast facing
slopes and coasts. Localized MVFR conditions are to be expected in
passing showers, but mountain obscuration is not expected to
become an issue.
Light sea breezes across Leeward Big Island this afternoon and
evening will promote cumulus buildups over the island's interior,
but a strong inversion at 7000 ft will limit max cloud top height
and shower intensity.
Fresh to locally strong easterly trades will continue through the
week as high pressure remains north of the area and a weak area of
low pressure passes to the southwest. Stronger winds will persist across
the typically windier locations from Maui County to the Big Island
due to terrain accelerations. The current Small Craft Advisory remains
in effect through Wednesday and will likely need to be extended through
the second half of the week. Heavy showers and a few thunderstorms
are possible across the leeward Kauai waters through tonight as the
Choppy surf will continue along east facing shores each day due to the
trades locally and upstream of the islands. A couple of south-southwest
swells will move through the local waters this week, but surf heights
will remain well below advisory levels. See the Collaborative Nearshore
Swell and Wind Forecast, SRDHFO, for additional details on swell
Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office