398 
FXHW60 PHFO 120641
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
841 PM HST Tue Apr 11 2023

.SYNOPSIS...
A strong high pressure system far north of the Hawaiian Islands 
will linger through Wednesday with breezy to locally strong trade 
winds continuing through mid week. This high will then weaken from
Thursday through Saturday producing more moderate trade winds 
across the island chain. Shower activity will favor windward and 
mountain locations, especially during the overnight and early 
morning hours each day through Saturday. As winds veer southeasterly
early next week, shower chances will decrease a bit before 
increasing again by mid-week as another low develops to the 
northwest of Kauai and slowly passes by just north of the 
island chain.

&&

.DISCUSSION...
The satellite water vapor channel this evening continues to show a
seasonably strong sub tropical jet stream over the islands. This
jet stream is positioned along the southern edge of a long and 
narrow upper level trough. Jet stream divergence will continue to
spread high cirrus clouds over the state through sunrise Wednesday
with diminishing ice crystal cloud coverage by afternoon as the 
jet slowly drifts eastward and moves away from the Hawaii region.

In the short range forecast, a strong high pressure system will
linger north of the state producing breezy to locally strong trade
winds through Wednesday. Upper level lows embedded within the
upper trough will continue to enhance trade wind shower activity 
across Hawaii likely through Thursday. One of these stronger lows 
will produce a low level trough near the Big Island and Maui on
Thursday, increasing moderate to locally heavy rain showers over 
these eastern islands. Chances for thunderstorms are also 
possible for the Big Island on Thursday with this system. 
Elsewhere, shower activity will trend higher over windward and 
mountain areas, especially in the overnight to early morning 
hours. Isolated showers remain in the forecast for most leeward 
areas. Slight decreasing shower trends are expected from Friday 
through Saturday as a weak ridge builds in over the islands. 

The long range forecast continues to suggest some changes in the
weather are on the horizon. Both the American (GFS) and European 
(ECMWF) show the high pressure ridge north of the islands breaking
down as a low pressure system near the Dateline dives south and 
sets up northwest of Kauai. Easterly trade winds will veer from a 
more southeasterly direction from Sunday into Monday and shower 
activity will decrease west of the Big Island due to the rain 
shadowing effects of southeasterly winds. Deeper tropical moisture
with southerly winds in the mid levels may enhance shower 
activity over Kauai and Oahu around the middle of next week. 

Slight changes in this forecast track of this low pressure system
will produce large changes in rainfall activity, mainly affecting
the forecast over the western islands from Kauai to Molokai. 
Weather model run to run consistency is fairly unsettled on this 
approaching system, therefore our confidence in the potential for 
heavy rain threats for any island next week remains low at this 
time. Stay tuned as these island by island rainfall impacts will
evolve over time and remain highly dependent upon the final 
position of this approaching low and cold front. 

&&

.AVIATION...
Moderate to locally breezy trade winds will carry bands of showers
off the Pacific towards east and northeast facing slopes and
coasts. Expect brief periods of MVFR conditions due to lower 
ceilings and reduced visibility in passing showers.

AIRMET Tango remains in effect below 8000 feet for occasional 
moderate turbulence over and immediately south through west of 
mountains for all islands. Strong directional shear aloft just 
north of Kauai could potentially bring severe turbulence. SIGMET 
Xray is in effect just north of Kauai where severe high level 
turbulence may occur this evening in the FL290 to FL400 range. 
This turbulence area will be decreasing and shifting away to the 
northeast this evening.

&&

.MARINE...
A strong high pressure cell located approximately 1,300 miles
north northeast of Oahu will remain nearly stationary the next
couple of days. The downstream pressure gradient created by this 
high as it slowly meanders east southeast through Friday will 
result in fresh to locally strong trade winds. This morning's 
ASCAT satellite pass just clipped Big Island and confirmed Small 
Craft Advisory (SCA) winds south of Big Island. Winds through 
smaller island bays and channels are likely near or frequently 
gusting to SCA threshold 25 knots. While the majority of the wave
energy resides in the short period wind wave spectrum, today's 
north swell has allowed what altimetry and buoy data have confirmed
to be SCA-level sea state conditions with nearshore seas heights 
reaching or exceeding 10 feet. Strong trades and/or rough seas 
will allow the all-water SCA to remain in effect through Wednesday
afternoon. A new high moving down from the Aleutian Islands will 
be absorbed into the high northeast of the states Friday. This 
will subtly weaken trades from Thursday onward. Moderate to locally
fresh trades will occur well into early next week. 

Recent buoy observations confirm that the 6 to 8 foot north (350 
degree) swell that peaked surf along north-facing shores this 
afternoon is on its way down. A small, medium period northwest 
(320 degree) swell is scheduled to arrive late this week. East- 
facing shores will experience rough conditions in response to 
several days of an upstream trade fetch producing higher short 
period wind wave chop. Surf along northeastern exposures will 
remain elevated as these shores receive the fading north swell and  
trade wind swell energy. East-facing shore surf may approach High
Surf Advisory (HSA) levels Wednesday. Small, background south 
swell energy will maintain knee to chest high surf along many 
southern shores through the week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Wednesday for all Hawaiian 
waters-


&&

$$

DISCUSSION...Bohlin
AVIATION...Bedal
MARINE...Blood

371 
FXHW60 PHFO 120650
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
841 PM HST Tue Apr 11 2023

.SYNOPSIS...
A strong high pressure system far north of the Hawaiian Islands 
will linger through Wednesday with breezy to locally strong trade 
winds continuing through mid week. This high will then weaken from
Thursday through Saturday producing more moderate trade winds 
across the island chain. Shower activity will favor windward and 
mountain locations, especially during the overnight and early 
morning hours each day through Saturday. As winds veer southeasterly
early next week, shower chances will decrease a bit before 
increasing again by mid-week as another low develops to the 
northwest of Kauai and slowly passes by just north of the 
island chain.

&&

.DISCUSSION...
The satellite water vapor channel this evening continues to show a
seasonably strong sub tropical jet stream over the islands. This
jet stream is positioned along the southern edge of a long and 
narrow upper level trough. Jet stream divergence will continue to
spread high cirrus clouds over the state through sunrise Wednesday
with diminishing ice crystal cloud coverage by afternoon as the 
jet slowly drifts eastward and moves away from the Hawaii region.

In the short range forecast, a strong high pressure system will
linger north of the state producing breezy to locally strong trade
winds through Wednesday. Upper level lows embedded within the
upper trough will continue to enhance trade wind shower activity 
across Hawaii likely through Thursday. One of these stronger lows 
will produce a low level trough near the Big Island and Maui on
Thursday, increasing moderate to locally heavy rain showers over 
these eastern islands. Chances for thunderstorms are also 
possible for the Big Island on Thursday with this system. 
Elsewhere, shower activity will trend higher over windward and 
mountain areas, especially in the overnight to early morning 
hours. Isolated showers remain in the forecast for most leeward 
areas. Slight decreasing shower trends are expected from Friday 
through Saturday as a weak ridge builds in over the islands. 

The long range forecast continues to suggest some changes in the
weather are on the horizon. Both the American (GFS) and European 
(ECMWF) show the high pressure ridge north of the islands breaking
down as a low pressure system near the Dateline dives south and 
sets up northwest of Kauai. Easterly trade winds will veer from a 
more southeasterly direction from Sunday into Monday and shower 
activity will decrease west of the Big Island due to the rain 
shadowing effects of southeasterly winds. Deeper tropical moisture
with southerly winds in the mid levels may enhance shower 
activity over Kauai and Oahu around the middle of next week. 

Slight changes in this forecast track of this low pressure system
will produce large changes in rainfall activity, mainly affecting
the forecast over the western islands from Kauai to Molokai. 
Weather model run to run consistency is fairly unsettled on this 
approaching system, therefore our confidence in the potential for 
heavy rain threats for any island next week remains low at this 
time. Stay tuned as these island by island rainfall impacts will
evolve over time and remain highly dependent upon the final 
position of this approaching low and cold front. 

&&

.AVIATION...
Moderate to locally breezy trade winds will carry bands of showers
off the Pacific towards east and northeast facing slopes and
coasts. Expect brief periods of MVFR conditions due to lower 
ceilings and reduced visibility in passing showers.

AIRMET Tango remains in effect below 8000 feet for occasional 
moderate turbulence over and immediately south through west of 
mountains for all islands. Strong directional shear aloft just 
north of Kauai could potentially bring severe turbulence. SIGMET 
Xray is in effect just north of Kauai where severe high level 
turbulence may occur this evening in the FL290 to FL400 range. 
This turbulence area will be decreasing and shifting away to the 
northeast this evening.

&&

.MARINE...
A strong high pressure cell located approximately 1,300 miles
north northeast of Oahu will remain nearly stationary the next
couple of days. The downstream pressure gradient created by this 
high as it slowly meanders east southeast through Friday will 
result in fresh to locally strong trade winds. This morning's 
ASCAT satellite pass just clipped Big Island and confirmed Small 
Craft Advisory (SCA) winds south of Big Island. Winds through 
smaller island bays and channels are likely near or frequently 
gusting to SCA threshold 25 knots. While the majority of the wave
energy resides in the short period wind wave spectrum, today's 
north swell has allowed what altimetry and buoy data have confirmed
to be SCA-level sea state conditions with nearshore seas heights 
reaching or exceeding 10 feet. Strong trades and/or rough seas 
will allow the all-water SCA to remain in effect through Wednesday
afternoon. A new high moving down from the Aleutian Islands will be 
absorbed into the high northeast of the state Friday. This will 
subtly weaken trades from Thursday onward. Moderate to locally fresh 
trades will occur well into early next week. 

Recent buoy observations confirm that the 6 to 8 foot north (350 
degree) swell that peaked surf along north-facing shores this 
afternoon is on its way down. A small, medium period northwest 
(320 degree) swell is scheduled to arrive late this week. East- 
facing shores will experience rough conditions in response to 
several days of an upstream trade fetch producing higher short 
period wind wave chop. Surf along northeastern exposures will 
remain elevated as these shores receive the fading north swell and  
trade wind swell energy. East-facing shore surf may approach High
Surf Advisory (HSA) levels Wednesday. Small, background south 
swell energy will maintain knee to chest high surf along many 
southern shores through the week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Wednesday for all Hawaiian 
waters-


&&

$$

DISCUSSION...Bohlin
AVIATION...Bedal
MARINE...Blood