Area Forecast Discussion

SYNOPSIS

Moderate trade winds will focus clouds and showers over windward and mauka areas through Saturday, along with allowing for the development of typical afternoon showers over the kona slopes of the Big Island. The tail end of a front will try to move down the island chain late Sunday through Monday, bringing breezy northeasterly trades and drier air in its wake. Then breezy easterly trades will bring periods of windward and mauka showers through the rest of the week.

DISCUSSION

Radar and satellite imagery show moderate trade winds focusing low clouds and showers over windward and mauka areas across the state this afternoon as trades finally fill in across the Big Island. With abundant tropical moisture lingering over the region, isolated heavy downpours will remain possible over the Big Island through this evening, where the greatest moisture and instability persist. Heading into Friday, model soundings show more stable conditions developing, leading to a more typical trade wind pattern through the weekend with shallow passing windward and mauka showers.

The next pattern change arrives late Sunday into Monday as an upper-level trough sweeps across the north-central Pacific and the tail end of a frontal boundary attempts to push down the island chain. An increase in windward and mauka showers can be expected ahead of and along this boundary, with breezy northeast winds and drier air filtering in its wake as high pressure builds to the north. This will bring welcome relief from this week's muggy conditions, with dew points projected to drop into the lower 60s on Monday and Tuesday.

The surface high north of the state will become elongated as a broad low pressure system tracks across the North Pacific, maintaining breezy easterly trades across the islands through the workweek. As batches of moisture filter through on the trades, periods of enhanced windward and mauka showers can be expected. One of these upticks in shower activity looks to occur midweek as increased moisture moves in on the trade wind flow and a weak mid-level shortwave trough adds some instability as it sweeps across from the east.

By next weekend, noticeable model spread emerges between the GFS and ECMWF. While trade winds look to persist, questions remain regarding their strength and how much moisture theyll bring to the area. The GFS continues to hint at a tropical cyclone developing far southeast of the state, whereas the ECMWF does not. The National Hurricane Center continues to monitor this area, maintaining a medium (40 percent) chance of development over the next 7 days.

AVIATION

Greatest coverage of -SHRA is over windward areas of the Big Island and Maui. VFR is predominant with brief periods of MVFR with any passing -SHRA. A moderate trade wind pattern remains into Saturday with VCSH/-SHRA for windward areas.

AIRMET Sierra for mountain obscuration remains in effect abv 020 for north through east areas from Oahu to Big Island. Conditions have only shown slight improvement, therefore will continue and reevaluate later in the afternoon and early evening.

MARINE

High pressure to the north will bring moderate to fresh trades to the region into the weekend. As the trades build, a Small Craft Advisory will likely be needed for the typical windier waters, and an incoming north-northwest swell will bring seas in excess of 10 feet to exposed waters.

The current small, short period north-northeast swell will maintain small surf along north-facing shores into Saturday. A larger, long-period northwest swell is expected to arrive late Saturday and will bring advisory level surf to north and west facing shores exposed to the swell Sunday into Monday. The swell is expected to shift slightly more northerly and may briefly build further on Monday before dropping Tuesday. Depending on the exact direction, a Marine Weather Statement may eventually need to be issued to due the potential for harbor surges at Kahului and Hilo during that time.

The current small, medium period south swell will gradually decline through the weekend. During the first half of next week, south shore surf will return to below seasonal averages. East- facing shores will get continue to be boosted due to the wrap from the north and southerly swells. As the larger north swell builds in Sunday night and Monday, the wrap from that will have the potential for advisory level surf during that time.

FIRE WEATHER

Recent rain and light to moderate trade winds will maintain low fire weather concerns through Saturday. As a weak front passes through early next week and brings breezy northeasterly winds and drier air to the region, fire weather concerns will become moderate.

HFO WATCHES / WARNINGS / ADVISORIES

None.