| Current Conditions | ||
| Temp |  | 2.8 C |
| RH | | 37 % |
| Wind | | W 0 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 217 FXHW60 PHFO 201339 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 339 AM HST Sun Oct 20 2019 .SYNOPSIS... Lighter winds are expected through tonight, with some afternoon sea breezes possible over Kauai and Oahu. Showers will continue to favor windward and mauka areas, but increased moisture over Kauai and Oahu could lead to more showers across these islands through tonight. Moderate trades are expected to return Monday and Tuesday. && .DISCUSSION... Have made some changes to the forecast through tonight to account for higher precipitable water (PW) values that are forecast to reach Kauai and Oahu. Have also weakened winds a bit over Oahu this afternoon and overnight. The ridge to the north of the islands is being pushed southward by a front to the northwest of the islands. Some southeasterly winds are already making it into the islands, and expect more of that today as the ridge moves closer to the region. That being said, the latest high resolution models show winds remaining a bit stronger over areas near Maui County and the Big Island today than originally thought. Satellite derived PW continues to show increased moisture moving into the waters to the southwest of the islands. An isolated thunderstorm was noted south of the Kauai coastal waters within the last hour, and have added the slight chance of thunderstorms to some of the nearby coastal waters for today. The morning soundings at Lihue and Hilo had PW values of 1.52 and 1.68 inches respectively. Normal for October is around 1.4. Models show PW will increase over Kauai and Oahu to between 1.7 and 2.0 inches, which is above normal. Near normal 500 mb temperatures are expected, but as the nearby thunderstorms show, with enough PW, thunderstorms aren't out of the question. For now will hold off on bringing any mention of thunderstorms over the islands, but will be monitoring the situation. With the increasing moisture, have boosted PoPs over Kauai and Oahu, and the adjacent waters through tonight. There is disagreement with the various models as to how much of a chance there was for rain, but ultimately decided to trend things up through tonight. The front is expected to pass by to the north over the next 24 to 36 hours, with the ridge retreating to the north as it lifts to the north. This will allow the winds to become more easterly and increase Monday and Tuesday. As this happens, we'll see more typical trade wind showers. Another front passing to the north could weaken winds during the second half of the week. At this time, there is no increasing in PW during that time, so the main question will be if winds go light enough to support local land and sea breezes. && .AVIATION... Moderate easterly trade winds will gradually shift out of the east-southeast direction through the day today. Lightest winds are expected over the northwest islands with this pattern, which may be light enough for sea breezes to develop over portions of Kauai and Oahu this afternoon. Although the bulk of the clouds and showers will continue to favor windward and mountain locations, afternoon showers associated with sea breezes will be possible over interior areas of Kauai and Oahu. No AIRMETs are in effect or anticipated at this time. Brief MVFR ceilings and visibilities are possible in and around passing showers. Otherwise, VFR conditions will prevail for all areas. && .MARINE... A surface ridge extending southwestward from a high to the distant northeast will move south and weaken today as a front approaches from the northwest. Although trade winds will diminish and veer to the east-southeast near Kauai and Oahu in response, moderate to locally fresh easterly trade winds elsewhere will continue to be sufficiently strong to warrant a Small Craft Advisory (SCA) for waters around the Big Island today. Increased moisture associated with a disturbance passing south of the area will bring a slight chance of thunderstorms to waters south and west of Kauai today. The front will stall well north of the islands tonight and dissipate Monday, allowing the ridge to move north and strengthen, likely leading to an expansion of the SCA to include other typically windy zones by Tuesday. Another front approaching late in the week may once again lead to diminishing winds. Surf is expected to remain below advisory levels along all shores through the upcoming week. A small north-northwest swell will diminish further today into Monday, with a new northwest swell is possible Thursday into next weekend. A new long-period south swell has moved in over the last 12-24 hours, with this swell expected to linger into Monday before diminishing. Trade winds will push short-period wind waves onto east facing shores for at least the next couple of days, trending down later in the week. See the Collaborative Nearshore Swell and Wind Forecast (SRDHFO) for more details on surf and swell sources. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST this evening for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...M Ballard AVIATION...Gibbs MARINE...Birchard Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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