Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 83 near the shore to around 71 above 3000 feet. Northeast winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers after midnight. Lows around 68 near the shore to around 58 above 3000 feet. Northwest winds around 10 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Breezy. Mostly sunny with isolated showers. Highs around 83 near the shore to around 71 above 3000 feet. East winds around 10 mph shifting to the west 10 to 20 mph in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny. Scattered showers in the afternoon. Highs around 82. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 67. Northeast winds around 10 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 79 to 84. Northeast winds 10 to 15 mph increasing to 15 to 25 mph in the afternoon. Chance of rain 50 percent.

Kaua’i Mountains

Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 70 to 78 in the valleys to around 64 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 40 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 58 to 63 in the valleys to around 52 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 70 to 77 in the valleys to around 64 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 82. East winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 40 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 61 to 70. Northeast winds up to 10 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 75 to 82. East winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 74 to 82. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 59 to 71. North winds around 10 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 74 to 82. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trade winds will gradually strengthen the next couple of days, delivering a few windward showers. Trade wind speeds will likely peak on Tuesday, becoming locally strong and gusty. Winds will diminish and become light Thursday and Friday as a front approaches, with continued limited rainfall. The front will likely dissipate near the islands over the weekend, with light to moderate trade winds returning.

Discussion

After a recent period of beneficial rainfall, island weather will be on the drier side over the next week, especially over leeward areas.
Light (to locally moderate) trade winds are delivering a cluster of low clouds and showers to windward portions of the Big Island and Maui this morning, while the remainder of the state is under mostly clear skies. Wettest locations in windward Big Island received about .5″-.75″ of rain overnight. The clouds appear rather innocuous in infrared imagery, but surface observations indicate low cloud bases with embedded areas of light to moderate rain and low visibility. This area of clouds is expected to weaken as it moves W today, but will bring a chance for windward showers, especially to Maui and Hawaii counties.
The trade winds are being supported by surface highs to the distant NW and NE, while a weakening and lingering trough NW of Kauai is keeping the local pressure gradient on the looser side. As the trough weakens and the high to the NW moves E through Monday, trade winds will gradually strengthen, favoring a NE direction over Kauai and Oahu. Trades will likely be strongest on Tuesday as the high passes N of the islands, with the potential for a Wind Advisory where winds are most accelerated by terrain. The high will push a frontal band toward the islands from the N, but guidance indicates it will stall N of Kauai. A trough aloft is currently over the E end of the island chain, but will soon be replaced by a ridge aloft building in from the W. Thus the strengthening trade winds are not expected to bring much more than a few brief windward showers that favor nights and mornings.
Late Wednesday and Thursday, developing strong low pressure to the N will force the high eastward, with the associated ridge extending over the islands from the NE. Winds will weaken and become light and variable through Friday as a front associated with the low approaches from the NW, with continued mostly dry weather expected. The front may bring a brief period of increased showers to Kauai and Oahu early next weekend before dissipating, with light to moderate trade winds and limited showers returning thereafter.

Aviation

Light to moderate trades will persist through today, then strengthen tonight into Monday as high pressure builds north of the state. Land breezes have developed overnight, and sea breezes can be expected to develop in sheltered leeward areas during the day today. Any showers that develop will be isolated to scattered in nature, and VFR flight conditions are expected to prevail for most locations throughout the forecast period. However, MVFR conditions have been prevailing at PHTO all night and will likely persist into the morning hours as trades continue to bring in some lower clouds and showers to mainly the eastern end of the state.
AIRMET Sierra for mountain obscuration is in effect for the eastern slopes of the Big Island through this morning, and is expected to improve by this afternoon. Eastern slopes of Maui may also need an AIRMET Sierra for mountain obscuration this morning if lower clouds and showers persist.

Marine

Weak ridging north of the state has maintained a lax pressure gradient over the local waters. This synoptic scenario has resulted in light to gentle trade winds. Weak high pressure to the north will allow this lighter trade pattern to remain unchanged through Monday. A better established area of high pressure northwest of the islands builds in behind a hurricane force low that will be tracking due east across the North Pacific and into the Gulf of Alaska through early Monday. This set up will tighten the pressure gradient down across the region and ultimately restrengthen trades from fresh to locally strong magnitudes by Tuesday afternoon. These speeds will hang on through Wednesday before backing off again in response to the high north of the islands moving east and being replaced by an area of low pressure. This low may be far enough south to drag a very weak, diffuse boundary into the waters by next weekend. A potentially large swell created by the hurricane force low positioned near 44N164W this morning will send a large enough swell down our northwest great circle route and into our offshore waters Monday to prompt Small Craft Advisories (for seas) by as early as tonight. This will occur just before the period of strong winds commences Monday night into early Tuesday across the typical windier waters surrounding Maui County and Big Island.
The High Surf Advisory (HSA) has been extended in time for the north and west-facing shores of the smaller islands and is now in effect through Monday afternoon. This is a result of this morning's passing northwest (320 degree) long period swell. Recent nearshore buoy observations indicate that this long period (15-17 second) 7 to 8 foot swell is already a couple of feet above guidance. This swell will peak today and result in solid HSA level surf through Monday as it forecast to be slow to subside. The next north northwest (330-350 degree) swell will be on the heels of today's swell, generated from the hurricane force low mentioned above, and is scheduled to arrive late Monday and peak Tuesday. This large, long period swell will likely drive surf heights to above High Surf Warning thresholds Tuesday. This large swell should slowly decline from Tuesday night through the remainder of the week as it veers more northerly. Strengthening trades should increase eastern exposure chop and lead to rough surf from Tuesday into the middle of the week. Small background swell leading to very small surf will continue along south-facing shores throughout the week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Monday for north and west facing shores of Niihau, Kauai, Oahu, Molokai and for north facing shores of Maui.

Data Courtesy of NOAA.gov