352 
FXHW60 PHFO 020157
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
357 PM HST Mon Apr 1 2019

.SYNOPSIS...
A weak front currently over Kauai will reach Oahu late tonight or
Tuesday then stall and dissipate. The front will produce modest
showers over north facing slopes, while most of the state will be
somewhat dry tonight. Moderate trade winds will return on Tuesday
as high pressure builds north of the state. Light showers will 
favor windward and mauka areas Tuesday through Thursday. Trade 
winds are expected to break down again on Friday and into the 
weekend. 

&&

.DISCUSSION...
A weakening front is draped across Kauai this afternoon, and an 
upper level trough passing overhead is generating some
instability. The ragged and shallow front is producing showers
along north facing terrain of Kauai. The upper level trough has
been producing a narrow band of mid level lift over Oahu through
much of the day, leading to a couple of thunderstorms earlier. 
The trailing edge of this band is moving over Oahu now, which will
lead to a diminishing thunderstorm threat through the remainder 
of the afternoon. With low level moisture lacking on Maui County, 
sea breezes have produced only a few showers today. On The Big 
Island, low level moisture pooled around a weak trough to the east
has fueled spotty showers over mainly the Puna and Hilo 
Districts, but no thunderstorms have been observed, in spite of 
somewhat unstable conditions revealed by the afternoon sounding. 
The upper level trough is also producing strong winds over the 
high summits of the Big Island where a Wind advisory remains in 
effect through tonight.

The dissipating front will remain over Kauai this evening, reach 
Oahu late tonight, and then stall on Tuesday as the upper level 
trough moves east of the state. Northeast winds will gradually 
strengthen as high pressure builds to the northwest of the 
islands, and the atmosphere will slowly stabilize as the upper 
trough exits. As a result, expect modest rainfall along most 
windward slopes. The dissipating front will produce a few more 
showers on windward Kauai in the evening and on Oahu late tonight 
and Tuesday, while there could be some lingering shower activity
and perhaps a thunderstorm on windward Big Island this evening. 

A stable, moderate to locally breezy trade wind flow is due on
Wednesday and Thursday. Surface high pressure passing about 300 
miles north of the islands will drive the trades, and a ridge 
aloft will produce stable conditions. This will result in light 
showers over windward slopes and dry leeward conditions.

The trade winds will likely break down again heading into Friday.
An approaching front will weaken and depress the surface
subtropical ridge southward, leading to the disruption in the
trades. A weak mid level ridge should hang on, and low level 
moisture should be near or below seasonal normal over most 
islands. This points toward a stable land and sea breeze pattern,
with clouds and only isolated interior showers, mainly each 
afternoon through at least Saturday. 

Uncertainty increases heading into Sunday. The ECMWF continues to
hold the front north of the islands, while the GFS, which has yet
to show run-to-run consistency, suggests that the front may reach
the islands. Both models suggest a return to trade winds on
Monday. 

&&

.AVIATION...
A weak front, near Kauai, will continue to slide southeast down 
the island chain this evening and eventually dissipate tonight.  
Slightly elevated levels of moisture and instability ahead of the
feature will lead to additional showers, mainly over Kauai, Oahu,
and NE sections of the Big Island. 

Tonight, as the front draws near, winds will begin to veer north 
northeasterly then northeasterly by Tuesday. 

No AIRMETS are currently in effect.

&&

.MARINE...
A weak front located over Kauai waters will gradually move SE 
toward Oahu tonight and dissipate by Tuesday. High pressure 
building N of the area will support a switch to moderate to 
locally fresh N to NE winds as the front passes and dissipates. 
This high will move very slowly toward the E through the week, 
supporting moderate to fresh trade winds that will veer from NE to
E from Tuesday through Thursday. Light and variable winds are 
expected Friday into Saturday as the ridge moves over the islands
once again, in advance of another approaching front. Thereafter, 
a process similar to that described above is expected, with the 
front dissipating near (or N of) the islands, and high pressure 
building to the N bringing a brief return of light to moderate N 
to NE winds late next weekend into early next week.

A Small Craft Advisory (SCA) will likely be required for windier 
areas around Maui and the Big Island as trade winds peak around 
midweek. Additionally, seas may reach the SCA criteria of 10 feet 
in waters around Kauai and Oahu Tuesday as an advisory-level 
mid-period NW swell arrives. 

A High Surf Advisory (HSA) has been issued for exposed north and 
west facing shores of the smaller islands starting tonight through
Tuesday night. This new swell should build tonight and peak 
Tuesday afternoon into Tuesday night before dropping below 
advisory levels on Wednesday. Another NW swell arriving Friday 
into the weekend may approach advisory levels. Forecast guidance 
has been inconsistent in the depiction of the source low's track, 
thus reducing confidence as to the specifics of the eventual swell
height seen in the islands. Otherwise, small surf will persist 
along south and east facing shores through the week. A slight 
increase is expected along east facing shores as trade winds 
strengthen middle of this week and a small Tasman Sea swell is 
currently providing a slight increase along south facing shores 
through Wednesday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory from midnight tonight to 6 AM HST Wednesday 
for north and west facing shores of Niihau, Kauai, Oahu, and 
Molokai and for north facing shores of Maui.

Wind Advisory until 6 AM HST Tuesday for Big Island Summits.

&&

$$

DISCUSSION...Wroe
AVIATION...JT
MARINE...Kino