Area Forecast Discussion
Issued by NWS Honolulu, HI

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXHW60 PHFO 040648
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
848 PM HST Fri Apr 3 2020

.SYNOPSIS...
An area of low pressure northwest of the state and a ridge of
high pressure to the east will keep a light wind regime in place
across the islands through next week. Showers will favor the
interior of the islands during the afternoon and evening hours.
Some deeper moisture will get drawn northward Sunday night through
much of next week, bringing the potential for periods of locally
heavy downpours and a few thunderstorms to the island chain.

&&

.DISCUSSION...
Currently at the surface, a ridge of high pressure is located
around 1200 miles northeast of Honolulu, with an area of low
pressure around 750 miles northwest of Kauai. Closer to the
islands, a nearly stationary frontal boundary is located around
275 miles northwest of Kauai. Light to moderate east-southeasterly
winds prevail around the Big Island, light southerlies near Kauai,
while light and variable winds are present across Oahu and Maui
County where daytime sea breezes are transitioning over to land
breezes. Infrared satellite imagery shows partly cloudy skies
across Kauai and Oahu, with mostly cloudy conditions across most
of Maui County and the Big Island. Radar imagery shows a few
showers moving into windward and southeast facing slopes of the
Big Island, the eastern tip of Maui, and south facing slopes of
Kauai. Very little, if any, shower activity is seen across Oahu
and the rest of Maui County. Main short term concern revolves
around rain chances during the next couple days.

The area of low pressure northwest of the state will intensify
over the next couple days, reaching between 990 and 995 mb by
Sunday evening. Meanwhile, the high pressure ridge axis northeast
of the islands will slide southeastward and closer to the islands.
This will result in a continued light southeast to south boundary
layer flow across the islands through the weekend, with overnight
land breezes and daytime sea breezes dominant. The low will lift
northeastward well to the north of the islands early next week,
while the high pressure ridge axis remains nearly stationary east
of the state. This will keep the southeast to south boundary layer
flow in place through Monday night, with a weak trailing frontal
boundary moving into the western islands on Tuesday. Light winds
will generally prevail through the first half of next week, with
daytime sea breezes and overnight land breezes remaining dominant.
Forecast confidence diminishes during the middle and latter part
of next week, as model consensus along with individual model run
to run continuity is struggling with pattern evolution details.
The latest trends suggest that a weak frontal boundary may waver
back and forth across the state, keeping a light wind regime in
place with daytime sea breezes and overnight land breezes
remaining dominant through the end of the week.

As for weather details, a few showers should continue to roll
into south facing slopes of Kauai and east and southeast facing
slopes of the Big Island tonight and through the morning hours
Saturday. Can`t rule out a shower trying to trickle into the south
shore of Oahu tonight and Saturday morning, as well as the eastern
tip of Maui, but overall very little shower activity is expected
across Oahu and Maui County through noon Saturday. Saturday
afternoon, with the high clouds east of the state, we should see
more daytime heating, with scattered showers developing over the
island interiors, with a thunderstorm or two not out of the
question on the Big Island. Most of the shower activity should
diminish in the evening, with a few showers continue to affect the
south facing shores of Kauai and Oahu, as well as east/southeast
facing slopes of the Big Island through Sunday morning. Low level
moisture will begin to increase by Sunday afternoon, which should
result in more daytime heating driven shower development over the
island interiors once again, with a thunderstorm or two possible
once again on the Big Island.

Sunday night through next Friday,
Deep moisture will begin to increase in the broad convergent flow
in advance of an approaching frontal boundary Sunday night through
Monday night, with precipitable water values climbing into the
1.5 to 1.7 inch range. The brunt of the shower activity should
remain over the western end of the state through Monday night,
although we`ll need to keep rain in the forecast statewide during
this time frame. Some of the showers could be locally heavy and
can`t rule out a few thunderstorms as well with some decent
shortwave energy moving through. The frontal boundary appears to
move into the western islands Tuesday, then stall out somewhere
across the central islands Tuesday night and Wednesday. The latest
guidance suggest the boundary may remain nearly stationary or
waver back and forth across the islands through the end of the
work week, with some locally heavy rainfall and even some
thunderstorms not out of the question. Long story short - the
pattern looks rather unsettled Sunday night through late next
week.

&&

.AVIATION...
The area west of Molokai is now under a light southerly low level
wind flow. With this said, we are expecting a few showers to
develop in this wind flow, either affecting or threatening these
two islands overnight. In fact, the Kauai NEXRAD is already
showing this with a couple of showers moving onto the south facing
shoreline around Hanapepe to Poipu. We do not expect the showers
to penetrate much further inland, as a offshore land breeze
develops in the coming hours. These showers will also threaten the
east facing shoreline as well. Brief MVFR ceiling and vis can be
expected with these showers.

Showers may also form over the waters south of Oahu after midnight,
threatening the island toward sunrise. Otherwise, fair skies and
VFR conditions will prevail. The dense high clouds will gradually
lift out from west to east as a short wave passes through. We
expect the bulk of the high cloudiness to be east of the Big
Island by sunrise Saturday.

Little change into Saturday as a light southerly wind flow
persists west of Molokai, and a mainly variable, on-shore flow
forms elsewhere. With day time heating, isolated to scattered
showers will arise over the interior areas of all islands.

AIRMET Tango for light to moderate turbulence between fl290 and
fl400, will continue beyond 1600z, in association with a jet stream.

&&

.MARINE...
The current light wind regime is expected to continue well into
next week. The overall background flow will generally be from the
southeast to south as a front slowly approaches the area from the
northwest. No Small Craft Advisory conditions are in the forecast
into the middle of next week.

A broad area of convergent southeast to south flow is expected to
set up over the state from late this weekend into early next
week. This will likely result in a period of unsettled weather
with locally heavy rainfall, and possibly thunderstorms.

A new north-northwest swell spreading across the area starting
early Saturday will produce moderate surf along most north and
west shores from late Saturday through Sunday. A new long period
west-northwest swell will likely arrive Sunday night, which will
keep moderate surf along most north and west facing shores into
early next week. This will be followed by a reinforcing moderate
northwest swell arriving late Tuesday, which will likely peak
Wednesday, and then gradually lower on Thursday. Surf is expected
to remain below the High Surf Advisory (HSA) criteria along north
and west facing shores through the middle of next week.

The current southeast swell will continue to gradually subside
this weekend. Additional swells arriving from the Southern
Hemisphere are expected to maintain small background surf along
south facing shores through next week. The lack of trade winds
will keep only small surf along east facing shores through the
middle of next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Jelsema
AVIATION...H Lau
MARINE...Houston


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.