Daily Weather

Oct 22, 2014 4:01 AM HST

Synopsis
Tropical storm Ana continues to move away from the main Hawaiian islands. East southeast flow will prevail over main Hawaiian islands today. A high building far north of the area will bring moderate trade winds Thursday and Friday. Winds will weaken and shift out the east southeast again over the weekend as a front approaches from the northwest.

Discussion
Tropical storm Ana, located south of French Frigate Shoals, continues to move away from the main Hawaiian islands. A band of high clouds nearly separated from Ana will move across Kauai and Oahu this morning. Infrared satellite shows low level cloud motions indicative of east southeast flow across the main Hawaiian islands this morning. The Big Island is partly blocking the flow across the smaller islands, making winds relatively light.

Radar indicates scattered to numerous light showers coverage over the windward slopes and waters with a few of those showers reaching upper leeward slopes of the smaller islands. Showers increased overnight due to the moisture advecting from an old frontal boundary brushing against the windward areas. Early morning soundings from Lihue and Hilo show a stable atmosphere with relatively high precipitable water values of 1.77 and 1.54 inches respectively, part of the reason for the light but numerous showers streaming in.

An east to west ridge far northeast of the Big Island and the circulation around tropical storm Ana will combine to maintain gentle to moderate east southeast flow over the main islands today. With the east southeast flow partly blocked by the Big Island, winds will be light enough over the smaller islands for sea breezes to dominate this afternoon and bring some clouds and showers to leeward and interior areas. The afternoon showers could be a bit more active given the moisture in place, but stable atmospheric conditions should keep this rainfall on the lighter side. While showers will focus over windward areas this morning, as the sea breezes kick in for leeward areas expect to see a shift to more leeward and interior clouds and showers by afternoon.

Although winds will be rather light around the smaller islands today, the low level flow will remain stronger near the Big Island. The Hamakua coast and South Point will be susceptible to a bit stronger winds due to the orientation of terrain and wind flow.

The global models are in good agreement showing a surface high far north northwest of the area building southeast on Thursday, strengthening the trade winds to moderate to fresh breezes. The trades will persist through Friday focusing showers over windward areas with mostly dry weather over leeward areas.

The surface ridge will weaken and move south again over the weekend as a front approaches from the northwest. The winds over the main islands will weaken and shift out of the east southeast. That wind flow will likely bring scattered nighttime showers over windward areas and some clouds and showers over leeward areas in the afternoons.

Aviation
Early this morning, the area of enhanced moisture associated with an old frontal boundary has made its way into the northern coastal waters and is helping to produce scattered showers with tops between 8 and 12 kft. Mvfr cigs and vis are likely within these showers. Expect some of these showers to push over land, mainly windward and mauka areas, later this morning and afternoon, leading to periods of MVFR conditions. As this occurs, there is potential for the need to issue airmet sierra for mountain obscuration. Interior areas may once again experience afternoon cloud build ups as the light E to SE background flow will allow for localized sea breeze development. Otherwise, VFR conditions will prevail.

Marine
The current north swell will subside through tonight. Another small swell from the north northwest arrives Thursday and will continue through the weekend but surf from these swells will remain below the advisory levels at north and west facing shores. Only small surf is expected at south and east facing shores.

Winds and seas will remain generally below small craft advisory levels through the forecast period.

Watches/Warnings/Advisories
None.
None.

All surf height observations and forecasts are for the full face surf height, from the trough to the crest of the wave.

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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