A trough moving over the island chain from the west will bring clouds and showers to the state through tonight. An accompanying upper level disturbance provides the instability for the chance for thunderstorms and locally heavy rainfall. Conditions are expected to improve Thursday or Friday, with trade winds returning this weekend.
Showers and a few isolated thunderstorms are ongoing across the state this morning. The bulk of the rain has stayed over the central portions of the state with heavier rain moving towards Molokai, Lanai and Maui. Total rainfall that has fallen ranges from a half inch to 2 inches over portions of Oahu. Slow moving cells may become anchored along the terrain of the islands, which could lead to flash flooding anywhere. The High Wind Warning for the Big Island summits continues through noon. The Flood Watch will also continue and the possibility of extending it will be evaluated today. A few thunderstorms with localized damaging gusty winds may develop along the trough.
The threat of heavy rainfall will diminish Thursday and Friday. The jet stream aloft will lift to the north as the upper level trough moves to the west and an upper level low develops along the trough. The weak surface trough, with ample moisture will likely linger, providing a chance for spotty heavy showers.
Friday night into Saturday a brief period of trade winds may return as the lingering moisture associated with the trough is pushed south of the islands. The GFS and ECMWF are showing breezy northeast winds developing Sunday as a shallow front moves near or over the state.
The line of SHRA/+SHRA that affected Oahu early this morning will continue to push slowly eastward over Maui County and to a lesser extent the Big Island during the next several hours. Isolated thunderstorms are also embedded in this line. Expect periods of MVFR and IFR conditions associated with this activity with mainly -SHRA elsewhere. PHTO and PHKO will start to see rain moving within the next hour or two. Conditions will begin to improve from west to east through the day.
Surface winds remain generally weak. However, thunderstorms could bring brief gusty and erratic winds.
AIRMET Sierra for mountain obscuration remains in effect abv 020 for all islands due to the the widespread low clouds and pockets of moderate to heavy rain.
A vigorous surface trough extends over the coastal waters surrounding Maui County and Oahu today, while a broad surface low continues to meander roughly 800 nm northeast of the islands. Moderate to fresh easterly winds are ongoing north of the trough, with southeast to south winds south of the trough. Close to the trough, these winds could become locally strong, especially if a surface low deepens near the islands, and a Small Craft Advisory (SCA) is in place for waters around Maui County and Oahu through Wednesday evening. In addition, a few thunderstorms along the trough could produce erratic wind gusts in excess of gale force. The trough and possible low will weaken near the Big Island Thursday, allowing ridging to the north to drive moderate to fresh easterly winds over most waters and southerly winds near Big Island. The trough will move south of Big Island Friday, and moderate to locally fresh trades will prevail Friday night into the weekend. Stronger northeast winds may develop on Sunday and require an SCA.
A moderate, northwest swell will continue to fade today, allowing surf decline along north- and exposed west- facing shores. While this swell fades by Thursday, a small, short-period north-northeast swell will persist through the rest of the week, and is likely to see a bump tonight into Thursday with the arrival of reinforcing energy from the northeast. This will keep small surf going along north-facing shores and some east-facing shores. A larger, long-period northwest swell will arrive late Saturday and may push surf above the high surf advisory threshold Sunday and Monday.
A series of overlapping south-southwest swells will continue through the weekend. The current swell is expected to produce surf above seasonal averages today, with an additional pulse on Thursday maintaining above average surf into Friday. Surf along south-facing shores will decline gradually this weekend into early next week.
Surf along most east-facing shores will be dominated by wrapping north to north-northeast energy and a small, northeast swell that could produce periods of moderate surf. Trade winds return this weekend, leading to an increase in choppy, east shore surf through early next week.
Flood Watch through late tonight for all Hawaii islands-
High Wind Warning until noon HST today for Big Island Summits.
Small Craft Advisory until 6 PM HST this evening for Kauai Channel-Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel- Maui County Windward Waters-Maui County Leeward Waters-Pailolo Channel.
