National Weather Service Raw Text Product

Displaying AFOS PIL: AFDHFO Received: 2019-02-08 14:27 UTC


765 
FXHW60 PHFO 081427
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
427 AM HST Fri Feb 8 2019

.SYNOPSIS...
Windy conditions will develop today, with very windy and 
unsettled weather expected at times over the weekend as an area 
of low pressure strengthens and moves southward toward the 
islands. Unsettled weather may persist into the middle of next 
week as the low lingers in the island vicinity.

&&

.DISCUSSION...
Currently at the surface, a 1006 mb low is located around 475 
miles northeast of Honolulu, with a cold front extending south- 
southwestward through the Big Island. Meanwhile, a strong 1037 mb
high is centered around 1350 miles northwest of Kauai. Behind the
front moderate to locally breezy north to northwest winds have 
filled in, with moderate westerlies in advance of the front. 
Infrared satellite imagery shows partly cloudy skies in most
areas, with some pockets of enhanced cloud coverage over windward
locales. Radar imagery shows scattered showers moving into
windward areas of the smaller islands, with a few showers spilling
into leeward communities. Across the Big Island, most of the 
shower activity has now exited to the east of the islands. Main 
short term concerns of many, revolve around the dangerously large 
surf and potentially damaging winds expected over the weekend. 

Today, 
The area of low pressure northeast of the state will track 
steadily eastward today, dragging a cold front southeastward 
and away from the Big Island. Meanwhile, the high northwest of 
the islands will continue strengthen to around 1039 mb by this 
afternoon. The gradient across the state will tighten as a result 
of these two features, with windy northerlies developing across 
most of the state by late this afternoon. Based on the latest 
model guidance and upstream buoy observations, we have issued a 
Wind Advisory beginning at 2 PM this afternoon for all of the 
smaller islands. As for sensible weather details, scattered 
showers will continue across across north facing slopes and coasts
in the northerly flow regime, with mostly rain free conditions 
aside from a spill over light shower or some sprinkles in leeward 
areas.

For the Big Island summits, strong winds are expected to continue
today, although there may be a bit of a decrease in speeds later 
this morning through the afternoon hours if model solutions are 
correct. The Wind Advisory has been extended through 6 PM this
evening. 

Tonight through Sunday night, 
Model solutions remain in good agreement, showing a new area of 
low pressure developing well north-northeast of the state 
tonight, then deepening as it moves rapidly southward toward the 
islands Saturday and Saturday night. The low is then forecast to 
slow down and stall out a couple hundred miles north of the state 
Sunday and Sunday night. A surge of strong northerly winds is 
expected tonight into early Saturday, and the current Wind 
Advisory may need to be expanded to include the Big Island later
today. The winds are expected to trend briefly below advisory 
levels on Saturday, but the winds should ramp back up out of the 
northwest Saturday evening, then becoming very windy out of the 
west-northwest after midnight Saturday through at least Sunday 
evening. How strong the winds get will depend on the exact
strength and track of the low in proximity to the islands, but 
High Wind Warnings based on the latest guidances appear likely 
for at least portions if not the entire island chain late Saturday
night and Sunday. Given the unusual northwest thru west wind 
direction during the expected peak of the wind event, downed trees
and power outages will be a distinct possibility statewide, with 
the areas where the winds get funneled most effectively in these 
wind directions being the most susceptible. 

As for sensible weather details, periods of showery weather will
impact the islands with the showers favoring north and northwest
facing slopes and coasts. Given the strength of the winds and
elevated inversion heights, some of the showers will spread over
the terrain into the typically drier leeward areas as well. The
airmass will be plenty unstable given the cold temperatures aloft,
but the moisture depth is forecast to remain below 20 kft, so at
this time the probability of thunder although non-zero, appears
low. That said, with the strong winds aloft in place, as bands of
showers move through the islands squally weather can be expected,
and damaging winds within these squalls can't be ruled out.

For the Big Island summits, winds will increase tonight with High
Wind Warning level winds likely Saturday through the remainder of
the weekend. In addition, some wintry weather could occur mainly 
Sunday and/or Sunday night as some deeper moisture rotates through
the area. In fact, temperatures will likely be cool enough that 
some wintry weather could even occur at the highest elevations of 
Haleakala as well. 

Overall, this low is shaping up to be a high-impact event, 
bringing multiple weather hazards, and significant threats to life
and property. As such, we have attempted to highlight the most 
significant weather impacts in an ongoing Special Weather 
Statement (SPSHFO) - until such time that Watches and Warnings 
cover all of the expected impacts.

Monday through next Thursday,
Uncertainty in the forecast increases following the weekend 
storm, with the GFS and ECMWF continuing to display some
differences in the synoptic pattern evolution. Despite the
differences in the movement and track of the low to the north of 
the islands, they both indicate that unsettled weather will hold 
in place through much of the upcoming week. As a result, will keep
showers in the forecast even for the typically drier areas 
through the period. Trade winds don't appear like they'll return 
anytime soon, with the models showing a general west-northwest 
wind direction at moderate to locally strong speeds continuing 
through much of the new week.

&&

.AVIATION...
A low pressure system north of the islands will produce scattered
showers across the region. A high pressure ridge will build in 
over the islands today with increasing north to northeasterly 
winds for all TAF sites. VFR conditions will prevail over the 
next 24 hours.

No AIRMETs are in effect. AIRMET Tango will likely be issued 
later today as low level winds increase, producing moderate 
mechanical turbulence over and south through west of mountain 
ranges across the state.

&&

.MARINE...
A deepening low pressure system is forecast to develop far north 
of the region starting tonight, and then move rapidly south 
toward the state this weekend. This feature is expected to bring 
unprecedented impacts, with very hazardous, and potentially life- 
threatening, conditions spreading across most Hawaiian Waters from
this weekend into early next week. If experienced mariners are 
considering venturing away from protected waters this weekend, 
please prepare not only for very strong sustained winds and 
treacherous seas, but for the likelihood of extreme squally 
weather conditions. If in doubt, DO NOT GO OUT! 

Currently, increasing northwest to north winds are spreading down
the island chain from west to east. Near gale force winds may
eventually develop over the extreme western coastal waters, and a
Gale Watch remains in effect for the waters adjacent to Kauai 
County starting this evening. Note that across the northern 
Hawaiian Offshore Waters beyond 40 nm from the Hawaiian Islands, 
winds will likely reach gale force starting Saturday, and then 
possibly increase to storm force (at least 50 knots!) by Saturday 
night. A Small Craft Advisory (SCA) has been issued for most 
Hawaiian Waters for a combination of increasing seas and
strengthening winds. Expect the deteriorating conditions to 
eventually require either a SCA or a Gale Warning for all coastal 
waters from this weekend into early next week. 

A new large northwest swell continues to build according to 
observations at buoys 51101 and 51001 early this morning. This 
swell will cause surf to build today along most north and west 
facing shores of the smaller islands. Therefore, a High Surf 
Warning has been issued for increasing surf along north and west 
facing shores of Kauai, Niihau, Oahu and Molokai, and for north 
facing shores of Maui. Increasing surf may also require a HSA for 
west facing shores of the Big Island starting tonight or Saturday.
In addition, surf may eventually reach the HSA criteria along
north facing shores of the Big Island by late Saturday or Sunday.

By late Saturday and Sunday, the model guidance continues to 
insist that the increasing winds and captured fetch associated 
with a storm-force low pressure system will cause extremely large
and disorganized waves to spread across the coastal waters. The 
combined seas will become extremely high due to a combination of 
the longer period swell, and the huge wind waves generated by near
gale to gale-force winds over the coastal waters. 

There is also a strong potential for extreme harbor surges in
north and west facing harbors, as well as significant coastal 
inundation and beach erosion along north and west facing shores of
most islands this weekend. This event may bring unprecedented 
coastal flooding to north and west facing shores, so anyone with 
vulnerable ocean front property needs to complete their 
preparations for this event as soon as possible.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 2 PM this afternoon to 6 AM HST Saturday for 
Niihau-Kauai-Oahu-Molokai-Lanai-Kahoolawe-Maui Windward West-
Maui Leeward West-Maui Central Valley-Windward Haleakala-Leeward 
Haleakala.

High Surf Warning from 6 AM this morning to 6 AM HST Monday for 
Niihau-Kauai Windward-Kauai Leeward-Waianae Coast-Oahu North 
Shore-Oahu Koolau-Olomana-Molokai-Maui Windward West-Windward 
Haleakala.

Wind Advisory until 6 PM HST this evening for Big Island Summits.

Small Craft Advisory until 6 PM HST Saturday for Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui 
County Windward Waters-Maui County Leeward Waters-Alenuihaha 
Channel-Big Island Windward Waters.

Gale Watch from this evening through Saturday afternoon for 
Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward 
Waters.

Small Craft Advisory until 6 PM HST this evening for Kauai 
Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Bohlin
MARINE...Houston