textproduct: Honolulu

SYNOPSIS

Breezy trades will gradually weaken to moderate speeds by the latter half of the week, and become relatively light this weekend. Periodic showers will continue within the trade wind flow through Wednesday, mainly focusing over windward and mauka areas. After Wednesday, winds will weaken. This will support land and sea breeze development, and showers should increase in many leeward areas.

DISCUSSION

Radar and satellite show mostly cloudy skies with isolated showers at this time, mainly windward and mauka. High clouds were streaming rapidly from west to east over the eastern part of the state. Winds were averaging 5 to 15 mph with gusts to near 20 mph in the usually breezy spots.

Trades will continue at moderate to occasionally breezy speeds today, but are set to weaken starting tomorrow and continue weakening into the weekend. A large part of the reason for this weakening is a cold front associated with an upper level trough. This front will move southeast toward the state late this week, but it won't make it here. The front draws closest to the state Sunday (the day most likely to give us our weakest winds) but recedes back to the northwest afterward. The pressure gradient near us will weaken as this front gets close, then strengthen again as it moves back to the northwest. Late this weekend, a surface high to our northeast retrogrades well back into the Pacific after flirting with the coast of the mainland, and helps to invigorate our pressure gradient. This stronger pressure gradient will help bring the trades back up near moderate speed in about a week.

AVIATION

High pressure north of the islands will continue to sustain moderate to breezy trade winds through tonight. Showers will focus over windward and mountain areas, occasionally making it to leeward areas. Showers coverage will generally be higher during the night time and morning hours. MVFR conditions are expected within showers, while VFR prevails elsewhere.

AIRMET Sierra remains in effect for mountain obscurations for N through SE sections of Kauai. These conditions are intermittent, and will likely improve later in the morning.

AIRMET Tango is in effect for mechanical turbulence downwind of the mountains due to breezy trade winds, and this is expected to continue until midweek.

MARINE

A high pressure far northeast of the islands with an associated ridge stretching west about 600 nm north of Kauai, is driving fresh trades across the area. This high will be pushed eastward over the next several days, and its associated ridge will be displaced southward, resulting in the slow decrease in local trades. A Small Craft Advisory (SCA) is in effect for the typically windy waters around Big Island and Maui until 6PM tonight. Trades should be down into the moderate to locally fresh range and will continue to fall into the gentle to moderate category by Friday and may hold into the weekend.

A series of southern hemisphere swells will continue through the week with the largest due to arrive this weekend. Currently, a building long-period south swell is overlapping a fading medium- period swell. The bulk of the new swell energy was aimed east of Hawaii, which still leaves some uncertainty in resulting surf heights through this evening. Expect south shore surf to be around seasonal averages today, and then slowly declining Wednesday, followed by a smaller pulse of south-southwest swell Thursday and Friday.

A much larger south-southwest swell will arrive Saturday night and Sunday. A storm just southeast of New Zealand is producing a fetch of seas in excess of 40 feet aimed at Hawaii, and there is growing confidence that south shore surf will well exceed High Surf Advisory levels during the peak Sunday into early next week, with High Surf Warning conditions possible. This swell will coincide with the peak monthly tides and will likely lead to significant wave runup and impacts to coastal infrastructure.

Small west-northwest is possible over the next few days, while rough east shore surf slowly declines below seasonal averages.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 PM HST this evening for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.