Area Forecast Discussion
Issued by NWS Honolulu, HI
FXHW60 PHFO 272046 CCA
Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
1046 AM HST Thu Oct 27 2016
Locally breezy trade winds will continue through next week,
becoming stronger for the next few days due to a building high
to our north. Passing low clouds and showers carried by the trades
will affect mainly windward and mountain areas. An upper level
trough will move over the state this weekend, resulting in heavier
showers and wet trade wind weather into early next week.
Water vapor imagery shows a weak mid-level ridge over the state,
with a trough to the northwest. At the surface, high pressure is
located far north-northwest of the state, with a front in between
around 34N. 12z soundings from Hilo and Lihue show inversions of
7-8kft and precipitable waters of 1.1-1.2 inches, which is drier
than normal for this time of year. Early morning MIMIC total
precipitable water imagery shows the drier air across the state,
with a band of moisture south of the Big Island and across leeward
offshore waters. There is also a pocket of moisture with values
near 1.4 inches over the windward offshore waters east of Oahu.
The moisture associated with an old front has cleared south of the
state. Some rain gages reported rainfall amounts up to an inch
over the past 12 hours, with less over the last 3-6 hours as
conditions started to dry out. Clouds remain banked across
windward sections, with more typical trade wind showers expected
for today. The additional moisture noted upstream will spread
across the islands later today/tonight, enhancing trade showers
once again. Forecast soundings/cross sections show a minor surge
in moisture depth, but with the inversion remaining in place. We
will also see a surge in trade wind speeds as well. The high to
the north-northwest will shift to the southeast and weaken
slightly. However, the front between us and the high will
dissipate, bringing us more under the influence of the high and
lead to the stronger wind speeds.
Heading into the weekend, the upper trough currently to the
northwest will amplify and dig across the state this weekend, then
linger nearby through Monday. Falling mid-level temperatures will
help to erode the inversion and destabilize the atmosphere.
Showers will be more active this weekend, and with the strong
trade winds they will more frequently spread leeward as well.
The GFS and ECMWF are pretty similar with the overall pattern near
the islands through the forecast period. By Tuesday, a strong
mid-level ridge builds across the state from the west,
reestablishing the inversion and returning us to a more typical
trade wind weather pattern. Through a series of surface highs and
fronts passing far north of the state, the subtropical ridge
gradually shifts southward through next week. Late in the week the
ridge may approach the far northern offshore waters, with trade
wind speeds across the islands dropping to more moderate levels.
VFR conditions prevail at all TAF sites and these conditions are
expected to prevail through tonight. There may be some brief MVFR
conditions over windward slopes as moisture riding in on the
trades interacts with island terrain.
No AIRMETS are currently in effect, however there may be some
local low level turbulence over and south through west of
mountain ranges due to the trade winds.
With the expected increase in wind speeds, the current small craft
advisory already expands to include all coastal waters tonight.
Based on the recent consistency as to trade wind speeds, we have
extended the advisory through the weekend as well.
A series of small to moderate north and northwest swells will
fill in over the weekend and again toward the middle of next week,
but surf heights are expected to remain below advisory levels. A
long period east swell is possible this weekend from the distant
Hurricane Seymour in the Eastern Pacific. Furthermore, east facing
shores will see an increase in rough and choppy surf under the
strengthening trades, possibly approaching advisory level in the
next few days.
Small Craft Advisory until 6 PM HST Saturday for Oahu Windward
Waters-Oahu Leeward Waters-Kaiwi Channel-Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Small Craft Advisory from 6 PM this evening to 6 PM HST Saturday
for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward
Waters-Kauai Channel-Maui County Windward Waters-Maui County
Leeward Waters-Big Island Windward Waters.