Hilo

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 61 to 69 near the shore to 48 to 55 at 4000 feet. North winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 77 to 82 near the shore to around 65 at 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 62 to 69 near the shore to 49 to 55 at 4000 feet. West winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 71 near the shore to 45 to 51 near 5000 feet. Light winds. Chance of rain 50 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 84 near the shore to around 65 near 5000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 71 near the shore to 46 to 51 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 60 to 69 near the shore to 52 to 60 near 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 78 near the shore to 69 to 76 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 61 to 69 near the shore to 53 to 61 near 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Kohala

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 60 to 69 near the shore to 52 to 60 near 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 78 near the shore to 69 to 76 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 61 to 69 near the shore to 53 to 61 near 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

South Big Island

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 72 near the shore to around 50 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Monday: Mostly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 85 near the shore to around 65 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy with isolated showers. Lows around 72 near the shore to around 50 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 61 to 69 near the shore to 48 to 55 at 4000 feet. North winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 77 to 82 near the shore to around 65 at 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 62 to 69 near the shore to 49 to 55 at 4000 feet. West winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Waikoloa

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 71 near the shore to 49 to 54 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 87 near the shore to 62 to 69 above 4000 feet. North winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 69 to 74 near the shore to 49 to 54 above 4000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A plume of moisture moving through the state will produce some enhanced showers across the state through this evening. A deepening low will drop down northwest of the state through the first half of the week. This will disrupt the trade flow by Tuesday with southerly winds and introduce higher chances for showers across the state. The threat for heavy rain and isolated thunderstorms will likely increase over Kauai Tuesday through Wednesday.

Discussion

This afternoon's satellite and radar imagery shows enhanced showers developing over many leeward and mountain areas. This is the result of the afternoon sea breezes and some instability aloft. Rainfall rates of up to 2 inches have been seen on some of the showers this afternoon and we should generally begin to see the showers weaken this evening as the sun sets and as the weak trough begins to move away from the state tonight into Monday.
On Monday, we should return to more of a typical moderate trade wind day as the upper level trough shifts away from the state and a drier air mass moves in the lower levels of the atmosphere. Trade winds should be slightly weaker than today, which will once again allow for afternoon clouds and some scattered showers. But this time, any showers that do develop should remain lighter in intensity than the showers that developed today.
Starting Tuesday, we should see an upper level low northwest of the state drop further southward, which will cause the trade winds to weaken and veer toward the south. Light to moderate southeast to south winds over the state will bring increasing showers across the state with a large gradient in rainfall expected between the western end of the state and the eastern end. The Island of Kauai will be the closest to the low pressure system and should see the greatest rainfall from this event. Heavy rain will be the main concern and a Flood Watch may be needed for Kauai around the Tuesday through Wednesday time frame. With the latest QPF ensemble guidance coming into better agreement, the main moisture axis will likely stay just west of Kauai. Nonetheless, it would only take a slight shift more eastward for Kauai to be under the main moisture band. Even if the main band of rain stays just west, heavy downpours with isolated thunderstorms should be expected over Kauai during this time. For rest of the state, scattered showers with some moderate rainfall totals will be possible with higher rainfall amounts around Oahu. By Friday, the upper level low should lift further north and away from the state which should bring the return of stable conditions, although trade winds may not return till later in the weekend.

Aviation

Moderate trades will persist through this evening and weaken slightly heading into Monday, ushering clouds and showers into windward and mauka areas. Current radar and satellite imagery show clouds and showers forming downstream of each island, and with an east-southeast steering flow, some of these clouds and showers could drift into leeward sections of their respective neighboring islands through this evening. Winds will be light enough to support isolated sea/land breeze development that will bring additional clouds and showers to some leeward and interior areas during the afternoon hours through tomorrow and clearing of these areas overnight. MVFR/IFR conditions will be possible in any showers, otherwise VFR conditions should prevail.
AIRMET Sierra for mountain obscuration is in effect for windward sections of Oahu through the Big Island as showers persistently move in on the trades.

Marine

Moderate to locally fresh easterly trade winds will ease on Monday and veer southerly for Tuesday through Friday. Trades will decline slightly on Monday as a 1039 mb high centered far northeast of Hawaii weakens and surface trough develops about 650 nm northwest of Kauai. On Tuesday, the trough will deepen into a low about 500 nm northwest of Kauai, and moderate winds will veer out of the south across most waters, while moderate to fresh southeast winds develop around the Big Island and Maui. The low will also bring a chance of heavy showers and thunderstorms, mainly over the western end of the island chain. The low will lift northward on Friday, allowing winds to back out of the southeast statewide.
Small surf will prevail along north shores through much of the week. A north-northwest swell has been hovering around 3 feet at 12 seconds on the nearshore PacIOOS buoys today and will decline tonight and Monday. As this swell fades Monday night, another tiny northwest swell will fill in and maintain small surf into Wednesday. Minimal surf is expected later Wednesday through Friday, followed by another small pulse of northwest swell next weekend.
South shore surf will be near April average through tomorrow, followed by a larger south-southwest swell on Tuesday. The PacIOOS Kaumalapau buoy has been showing the current swell holding at around 2 feet 15 seconds this afternoon, with little change expected Monday. A larger swell will arrive on Tuesday, pushing surf along south facing shores above summer average. The swell will hold through Wednesday, then decline Thursday and Friday.
Small surf along east facing shores will be near current heights through Monday, then drop on Tuesday as southerly winds develop.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov