Daily Weather

Jun 11, 2015 10:00 AM HST

Synopsis
Weakening trade winds will diminish further on Friday, with sea breezes becoming more prominent by day and land breezes at night. Shower activity will shift from windward slopes mainly at night and during the morning to interior and leeward areas each afternoon, though rainfall amounts should remain modest.

Discussion
Water vapor imagery shows an upper level low northeast of the state, gradually moving northward, with a larger low far to the north. A ridge is located just north of the state between the two lows. At the surface, high pressure is located far to the north-northeast, with surface troughs to the east and to the far north-northwest of the state. 12Z soundings from Lihue and Hilo show weak inversions around 10kft. Precipitable waters range from 1.31 inches in Lihue to 1.13 inches in Hilo. Early morning mimic total precipitable water imagery shows pockets of similar moisture extending a couple hundred miles north and northeast of Kauai, with an area of drier air between 50 and 150 miles northeast of the remaining islands.

The upper level low northeast of the state has begun to move northward and weaken, eventually to be absorbed into the digging upper low well north of the state. As this occurs, weak subsidence associated with building mid-level heights will briefly help to strengthen and lower the inversion, though a lingering upper level trough over the northwest half of the state will keep the airmass somewhat unstable. Model cross sections show the current elevated moisture depth lingering into Friday before diminishing over the weekend. Rainfall amounts have been higher over kauai/big island, with a quarter to a third of an inch inch in the past 12 hours compared to a tenth of an inch elsewhere. A band of clouds approaching windward oahu/maui county will enhance windward showers this morning. Otherwise we should see an increase in interior/leeward showers this afternoon. Yesterday we had a few heavy showers develop across leeward Maui and Big Island. The atmosphere may be a bit more stable than yesterday, but the potential for localized heavy rainfall still exists.

12Z models show the high will shift northward and actually strengthen through the weekend. However, the surface trough to our east will shift northwest and pass between us and the high, keeping the gradient light across the islands. Initially the gradient will weaken slightly over on Friday, then further diminish over the weekend as a weak low develops north of the area along the trough. Light trade winds will give way to increasing sea breezes by the weekend. It appears that there should remain enough of a background gradient to keep some showers focused across windward sections at night, with the bulk of the clouds and showers occurring across interior and leeward sections during the afternoon and evening. A multi-model blend of precipitable water fields shows a downward trend from this evening into Friday, with below normal moisture values heading into the weekend. The drier and more stable airmass will limit rainfall amounts.

Aviation
Light to moderate trades will remain with VFR dominating the area. Clouds and showers embedded in the trade winds flow will favor windward and mountain areas, with isolated MVFR cigs/vis. Afternoon showers with tops to 15 thousand feet are possible along the leeward slopes of the Big Island and Haleakala.

Marine
Weak winds and small swell will keep conditions below the threshold for a small craft advisory through early next week.

Watches/Warnings/Advisories
None.

Advisory and Warning Criteria
Location Advisory Warning
North-Facing Shores 15 Feet (8') 25 Feet
West-Facing Shores - Big Island 8 Feet (4'+) 12 Feet
West-Facing Shores - Remaining Islands 12 Feet (7') 20 Feet
South-Facing Shores 8 Feet (4'+) 15 Feet
East-Facing Shores 8 Feet (4'+) 15 Feet

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