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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 261329

Area Forecast Discussion
National Weather Service Honolulu HI
329 AM HST Sun May 26 2019

A moderate and stable easterly trade wind flow will focus clouds
and showers across windward slopes through tonight, with mainly
dry conditions prevailing over leeward areas. The trades will
ease slightly Memorial Day through Wednesday, leading to increased
chances for afternoon sea breezes and a few showers across
leeward areas. The trades are expected to strengthen Thursday
into next weekend, bringing a return of more typical trade wind
weather featuring windward and mauka showers and the occasional
leeward spillover.


Currently at the surface, a 1025 mb high is centered around 1400
miles northeast of Honolulu, while a weak front remains nearly
stationary around 225 miles northwest of Kauai. The resulting
gradient is driving light to moderate trade winds across the
state early this morning. The morning soundings from PHLI and PHTO
showed inversion heights between 5.0 and 8.0 kft respectively,
with precipitable water values ranging from 1.1 to 1.5 inches.
Infrared satellite imagery shows a mix of low and high cloud
across the island chain, resulting in partly to mostly cloudy
conditions, with the most extensive cloud cover in windward
locales. Radar imagery shows scattered showers moving into
windward areas, with a few showers reaching leeward areas from
time to time. Main short term concern continues to revolve around
rain chances the next few days.

Model solutions are in good agreement showing high pressure
holding in place to the northeast of the state through the middle
of the week, while the stationary front lingers a couple hundred
miles northwest of the island chain. Moderate trade winds will
hold in place today, then ease slightly with boundary layer winds
shifting around to the east-southeast Memorial Day through
Wednesday. This will keep light to moderate east to east-
southeast winds in place across windward areas, while sea and land
breezes become common in many leeward locales. The stationary
front will dissipate around Wednesday, with high pressure then
strengthening and shifting closer towards the state through the
remainder of the week. This is expected to bring a return of
trade winds to the island chain by Wednesday night, with the
trades steadily strengthening to moderate and locally breezy
levels Friday into next weekend.

A fairly typical trade wind weather pattern will hold in place
through tonight, with showers favoring windward and mauka areas
and a stray shower reaching leeward communities from time to time.
The pattern will change slightly Memorial Day through Wednesday,
as sea breeze development in the more sheltered areas will result
in a few more showers developing each afternoon across leeward and
interior sections that will diminish during the evening hours.
There could be a few heavier showers as well due to the increased
moisture provided under the east-southeasterly boundary layer
flow. A transition back to more typical trade wind weather is
expected Wednesday night into next weekend, with showers favoring
windward and mauka areas, and the occasional leeward spillover.


A high pressure center far northeast of the Hawaiian Islands will
produce a surface ridge north of the state. This surface ridge
will keep moderate easterly trade winds in the forecast for most
airfields over the next 24 hours. Wind speeds will likely remain
just below the threshold for moderate turbulence downstream from
mountain ranges.

A stable high pressure ridge aloft will keep lower trade wind
inversion heights between 6000 to 8000 feet, limiting shower
activity to the isolated to scattered range. Any showers that
develop will favor the windward and mountain areas. Mostly VFR
flight conditions are expected.

No AIRMETs are in effect and none are forecast.


Winds are on the decline as the high far to the northeast slowly
weakens. As such, the Small Craft Advisory for waters near Maui
County and the Big Island has been cancelled with the morning
package. Expect lighter winds into Wednesday. A ridge building
north of the islands during the second half of the week should
allow winds to rebound to fresh to strong levels.

The incoming south swell appears to be leveling off, with the
resultant surf just below advisory levels. Will continue to
monitor reports today as this swell is expected to peak today and
Monday, before declining Tuesday. A new long-period, although
slightly smaller, south swell is expected to arrive Tuesday and
hold into the middle of the week. Additional small south swells
are expected during the second half of the week.

A small northwest swell associated with a gale that crossed the
dateline a few days ago is expected to begin to slowly ease
Monday through Tuesday. Another north-northwest swell is possible
Thursday. Surf along east facing shores will remain up through
the weekend due to the recent fresh to strong trades upstream of
the islands. Expect a downward trend early next week as the
trades weaken.





MARINE...M Ballard

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