Scientific Forecaster Discussion
fxhw60 phfo 210634
Area forecast discussion
National Weather Service Honolulu HI
834 PM HST Wed Feb 20 2019
lighter winds are forecast across the islands with dry conditions
over Kauai and Oahu. A surface trough will linger near The Big
Island over the next few days enhancing clouds and showers over
east Maui and The Big Island into the weekend. A high pressure
system moving into the central Pacific on Monday will bring breezy
north to northeast winds with a mostly dry weather pattern across
the state through Tuesday.
satellite imagery this evening shows layered clouds lingering over
The Big Island associated with a surface trough east of Hilo. Lower
level clouds are drifting into Maui and Lanai this evening.
Doppler radar shows mainly isolated shower activity within these
fairly stable cloud layers.
Short range model solutions are showing this trough axis will drift
westward over The Big Island tomorrow spreading scattered showers
into east Maui and scattered to numerous showers over the east
and southeastern sections of The Big Island into Saturday.
Otherwise a weak pressure gradient over Hawaii will produce local
scale land and sea breezes with increasing clouds over interior
sections each afternoon and clearing at night. A weak short wave
trough will pass over Maui and Hawaii counties from Saturday
night into Sunday morning, possibly producing deeper convective
showers over the eastern slopes of Maui and The Big Island.
Locally heavy showers may develop in some areas, however
confidence on locating these heavy rain impacts remain low this
Starting on Sunday the surface trough moves eastward as a strong
1030 mb surface high moves into the region from the west. Expect
gradually increasing north to northeast trade winds through the work
week as this high center approaches the islands increasing local area
pressure gradients. Clouds and a few showers from a shallow cold front
will pass through the state from west to east on Tuesday and Wednesday
likely increasing windward and mountain showers over all islands.
Strong and cold north to northeast trade wind push may develop on
Wednesday as the pressure gradient increases between the surface
high far north of Kauai and a cut off low deepening far to the
northeast of the island chain. Temperatures will fall a few
degrees and these stronger winds will cause clouds and showers to
favor windward and mountain areas through Thursday.
a surface trough will remain nearly stationary just east of The
Big Island overnight. Clouds continues to come and go over that
island, and there are a few showers at times brushing the puna
coastline. Satellite imagery and radar is picking up more mid
level clouds, between 11k and 15k feet, approaching The Big Island
from the south. Some of the low clouds is drifting over from
northern Big Island to adjacent eastern Maui. Do expect most of
these clouds to linger over these locations overnight and into
Thursday. A shower or two may also Spring up, mainly over the
waters overnight. Elsewhere looks even better with fair skies.
There was an isolated shower west of Wailua, Kauai, but this
shower is in the dissipating stage. We are anticipating a dry
evening overall, although the cloud cover will be thicker over The
The surface trough is expected to ease back to The Big Island on
Thursday. This will up the Prospect for showers across The Big
Island and Maui, especially in the afternoon.
Light winds will prevail across the area through Thursday. A land
breeze will dominate the wind flow overnight, then with daytime
heating, an onshore sea breeze fills in, leading to some afternoon
clouds over the land areas. As noted above, showers are expected
to affect primarily The Big Island, followed by Maui. Only
isolated showers are expected for the remaining islands Thursday
afternoon. The tops of the clouds are expected to rise from 6k
feet over Kauai to 12k feet over Maui to 20k over The Big Island.
No airmet in effect, and none is expected through Thursday
light and variable winds will continue across most Hawaiian waters
into the upcoming weekend. Overnight and early morning land breezes
followed by late morning and afternoon sea breezes will result near
the immediate coastal areas for each island. The exception will be
around The Big Island due to a trough of low pressure that is
forecast to shift westward back into the area Thursday through
Friday. Moderate to fresh breezes out of the southeast direction
will fill in across the windward and southeast Big Island waters
through the day Thursday, then continue through Friday. The best
chance for showers will accompany this trough of low pressure
across the Maui County and The Big Island waters.
Over the weekend, high pressure will build to the north in the wake
of a passing cold front. Moderate to fresh northerly winds will fill
in Saturday night through Sunday from west to east, then shift out
of a more typical trade wind direction and weaken through the day
Monday. A second front will approach and potentially move into the
area from the north Monday night through midweek, which could bring
fresh to strong north to northeast winds across the waters Tuesday
night into midweek.
Seas will remain at or around the advisory level (10 ft) over most
windward waters through the night due to a large short-period
easterly swell (9-11 sec periods) from a persistent area of strong
trades upstream of the state across the eastern Pacific. The evening
observations at the exposed nearshore pacioos buoys reflect this and
are holding around 10 ft at the Pauwela and Hilo stations. A
downward trend is anticipated Thursday into the upcoming weekend
as this area of strong winds trend down.
Surf along east facing shores will hold through Thursday around
advisory levels (8 ft), then gradually ease into the weekend as
the swell lowers. The high surf advisory in place will continue
through Thursday as a result, then likely be lowered beginning
Thursday night or by Friday.
After a long stretch of large surf and northerly winds for our north
facing shores through the first half of February, surf will near a
minimum for the month through the weekend. Storms over the far
northwest Pacific have been quickly lifting north-northeast from
Japan to the Bering Sea, ultimately limiting our traditional setup
for northwest swell sources.
An upward trend is expected next week in response to a potential
powerful hurricane-force low projected to develop off the coast of
Japan Saturday, then race northeastward toward the Aleutians/date
line Sunday. Wavewatch iii and the European model (ecmwf)-wave solutions depict a
large long-period northwest (320 deg) swell evolving from this
source moving through the Hawaiian waters Tuesday night through
midweek. If this materializes, surf could near warning levels for
exposed north and west facing shores Wednesday through Thursday.
Additionally, strong northerly winds accompanying a cold front
moving down the island chain during this time will result in
rough conditions with Small Craft Advisory winds and seas.
high surf advisory until 6 PM HST Thursday for Kauai windward-
Oahu koolau-Olomana-Molokai windward-Maui windward west-windward
Haleakala-south Big Island-Big Island north and east.
Wind Advisory until 6 am HST Thursday for Big Island summits.
Small Craft Advisory until 6 am HST Thursday for Oahu windward
waters-Kaiwi Channel-Maui County windward waters-Alenuihaha
Channel-Big Island windward waters-Big Island southeast waters.