| Current Conditions | ||
| Temp |  | 4.3 C |
| RH | | 11 % |
| Wind | | SW 21 mph |
| Road | | Open (4x4) |
|
Menu of Text Products for the Hawaiian Islands and the Tropical Pacific/Atlantic Oceans: |
|
Narrow the Menu List Select Time Limit: 12 hours | 24 hours | 48 hours | 72 hours | No time limit Select Product Type: All | Routine Bulletins/FCSTS | Warnings/Watches/Advisories | HAWN Weather | Tropical | Marine | Aviation | Daily Obs | Special |
|
|
Hawaiian Islands Synoptic Discussion and Guidance 532 FXHW60 PHFO 191401 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 401 AM HST Tue Mar 19 2019 .SYNOPSIS... A high pressure system will drift eastward today passing just north of the Hawaiian Islands, keeping moderate trade winds in the forecast. Dry stable air aloft will limit shower activity for much of the week. On Wednesday, a trough associated with a cold front approaching the islands from the north will weaken the ridge north of the islands producing light winds. High pressure will build back in over the region from Thursday onward with increasing trade wind speeds. A cold front will bring clouds and showers to the islands on Saturday and Sunday. Strong trade winds will arrive with the frontal passage. && .DISCUSSION... This mornings satellite imagery shows an extensive area of stable stratocumulus clouds that developed overnight around the Hawaiian Islands. These clouds will decrease in coverage through the morning hours and precipitation coverage will remain limited. Morning soundings from Lihue and Hilo are showing a strong trade wind subsidence inversion aloft around 5000 to 7000 feet capping vertical cloud development today. A surface high north of the state will drift into the East Pacific today keeping a dry moderate trade wind pattern in the forecast for today. As the high drifts east, a trough with an associated cold front moves into the Central Pacific basin weakening the ridge north of the islands on Wednesday. Surface pressure gradients will weaken in response to this approaching trough on Wednesday with onshore sea breezes forecast to develop over leeward coasts and slopes by Wednesday afternoon. On Thursday, another surface high builds in north of the state with a return to the trade wind flow and isolated to scattered showers over windward and mauka areas. Trade wind speeds will increase over the next two days, becoming breezy on Friday and locally windy on Saturday. On Saturday, the cold front arrives over the northwestern islands bringing in clouds and elevated showers to the islands of Kauai and Oahu. This front will slowly spread south down the island chain on Saturday night, reaching the Big Island on Sunday. The arrival timing with this front will be tricky as the movement towards the islands will be driven by the low level winds blowing out of the high center behind the front. We had to delay the arrival timing of this front by roughly 12 hours this morning due to updated model guidance showing a slower and weaker front. Both the American (GFS) model and the European (ECMWF) model continue to show run to run timing differences keeping our confidence on start and stop times for this event squarely in the fair category. That said, stronger trade winds arriving with this system will enhance clouds and showers along windward and mountain areas. Some of the stronger showers will drift over leeward areas. For outdoor activities this weekend, plan for breezy to windy conditions with periods of rain showers. Weather conditions will improve after frontal passage. Some clouds and scattered showers will linger over windward and mauka areas with slightly higher shower activity forecast during the overnight and early morning hours. Moderate trade winds will continue through the first half of next week. && .AVIATION... Today, surface high pressure north of the region will generate light to moderate easterly flow, generally veering to east southeasterly by this afternoon. Limited shallow moisture should allow for only ISOL -SHRA along the windward coasts and slopes. Otherwise, VFR conditions prevail at the local airports. && .MARINE... Moderate to fresh trades will continue today, then ease into the light to locally moderate range tonight through Wednesday night as a front passes by well to the north of the islands. A Small Craft Advisory (SCA) remains in effect for most waters today due to elevated seas associated with the current northwest swell, with all marine zones expected to drop below SCA levels tonight as this swell fades. A new northwest swell will build on Wednesday however, and this will likely bring seas back up to SCA levels across portions of the marine area exposed to this swell. The trades will begin to re-strengthen Thursday as a new high builds northwest of the state, reaching moderate to strong speeds Thursday night through the weekend. The increasing trades in combination with a series of overlapping northwest swells will likely require SCAs for a good chunk of the marine area Thursday through the weekend. Surf along north and west facing shores continues to slowly decline early this morning, but the latest buoy observations continue to support advisory level surf along most north and west facing shores. As a result, the High Surf Warning (HSW) for north and west facing shores of Niihau, Kauai, Oahu, Molokai and north facing shores of Maui has been cancelled and replaced with a High Surf Advisory (HSA) through 6 PM this evening. The swell has dropped below HSW and HSA levels along north facing shores of the Big Island, so the HSW has been cancelled here. Surf along west facing shores of the Big Island has dropped below HSA levels, so the HSA has been cancelled here. Surf is expected to drop below advisory levels along north and west facing shores of all islands early this evening. A new northwest swell will be hot on the heels of the current fading northwest swell however, and this will likely bring surf back up to advisory levels across north and west facing shores exposed to this swell once again on Wednesday. A series of overlapping northwest swells will keep surf elevated along north and west facing shores through the remainder of the week and over the weekend, with surf remaining near or at advisory levels Wednesday night through Saturday. Surf along east facing shores will remain small through midweek, then rise Friday into the weekend as strong trades return locally and upstream. Surf along south facing shores will remain small through the week with mainly background southerly pulses moving through. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 PM HST this evening for Niihau-Kauai Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu Koolau-Molokai-Maui Windward West-Maui Central Valley-Windward Haleakala. Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters- Kauai Channel-Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-Alenuihaha Channel-Big Island Windward Waters- Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Bohlin AVIATION...JT MARINE...Jelsema Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
|