Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly sunny. Isolated showers in the morning. Highs around 90 near the shore to around 78 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 74 near the shore to around 63 above 3000 feet. East winds around 10 mph.

Wednesday: Sunny. Highs around 90 near the shore to around 78 above 3000 feet. East winds around 10 mph.

South Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 90. East winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 74. East winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers in the morning. Highs 82 to 90. East winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Breezy. Partly sunny with scattered showers. Highs 76 to 87 in the valleys to around 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 65 to 73 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Wednesday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 87 in the valleys to around 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

North Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 90. East winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows 67 to 75. East winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers in the morning. Highs 78 to 90. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 75 to 87. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 78. East winds 10 to 15 mph. Chance of rain 40 percent.

Wednesday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 75 to 87. East winds around 10 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Moderate trade winds will strengthen some today, and remain locally breezy through the rest of the week. Lighter winds are possible by the weekend. Passing showers will favor windward areas, with some afternoon showers over the Big Island's leeward slopes.

Discussion

Several changes to the forecast were made with the morning package. The PoPs have been lowered a bit over the islands for the next several days, following the National Blend of Models (NBM) drier trend. Winds have been nudged upwards over the next couple of days as expected, keeping in line the NBM and other recent runs of high resolution models. This has prompted the issuance of a Small Craft Advisory for some coastal waters, see the Marine section for more details.
The synoptic features haven't changed much since last night. The mid-level low, along with its thunderstorms, have moved to the west, and is about 140 miles northwest of Kauai early this morning. The associated surface trough has also moved to the west, and this is allowing the trades to rebound a bit. The overnight ASCAT-C pass missed the islands, but the ASCAT-B clipped the eastern edge of the Big Island, and showed the upward trend that we were expecting.
As the mid-level low and its instability move to the west, the airmass over the islands is expected to become more stable, which will lead to a downward trend in shower activity. Thus the decrease in PoPs in the forecast as noted above. The trade wind regime will help to focus any showers to the windward slopes of the islands. Despite a more stable airmass overhead, some clouds and showers could form over the leeward slopes of the Big Island during the afternoon hours.
As expected with the mid-level low moving to the west, some high clouds are being carried to the northeast over the islands. Expect some of these high clouds to remain in the area for the next couple of days.Lighter winds are possible by next weekend as a new low passes north of the islands.

Aviation

Moderate trades will become locally breezy later today and continue to deliver clouds and isolated to scattered showers to windward and mauka areas. VFR conditions will generally prevail, but MVFR conditions will be possible in any showers.
No AIRMETs are currently in effect and none are anticipated to be needed today.

Marine

A trough of low pressure passing west over the far northwest offshore waters this morning may produce isolated thunderstorms over the far western Hawaiian Island waters through the day. Low pressure moving east across the Gulf of Alaska will ride atop a large area of high pressure centered north of the islands. This may push the high slightly closer to the islands but this will have little to no effect on moderate to locally strong trades the next several days. A Small Craft Advisory is in in effect for the windier waters surrounding Maui County and Big Island through Wednesday afternoon.
A small to moderate size, long to medium period northwest swell (320-330 degrees) arrived at the northwest offshore buoys last night and is timed to reach Kauai before sunrise, Oahu around sunrise. This swell will peak tonight into Wednesday morning and lift north surf to well above head high along those reefs and shorelines where northwest energy best focuses. Surf from this swell is expected to remain under the High Surf Advisory heights and gradually decline beginning Wednesday afternoon. Surf along south-facing shores may experience a series of small, long period southwest pulses at the end of the month in response to storms that are passing south of the Tasman Sea and New Zealand early this week. A very small fetch area of strong southwest winds about 1,000 miles southwest of Oahu in association with recent strong thunderstorm activity may bring in small period energy from the west southwest Wednesday into Thursday. East-facing shore chop should remain small through much of the week due to the lack of a strong trade fetch over or upstream of the state.

Fire weather

KBDI values remain near 626 today. The minimum relative humidity this afternoon could drop into the mid 40s today, while winds are on the uptick. This could bring us close to red flag conditions for a brief time this afternoon. Models show that afternoon relative humidity shouldn't be as low tomorrow afternoon, but winds will remain locally breezy through much of the week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov