Breezy trades will gradually ease through the rest of the week. Moisture embedded in the trades will allow showers to favor windward and mauka areas into Friday. An overall wetter pattern is expected this weekend as additional moisture is drawn over the island chain and an upper level disturbance moves overhead. Strengthening trades early next week will return a more typical windward and mauka focused shower pattern, followed by more stable conditions by mid to late week.
Radar and satellite imagery this afternoon show isolated to scattered showers moving into most windward areas on breezy to locally windy trade winds. The motion of these showers continues to indicate a slight southeasterly component in the low-level steering flow, a pattern that is expected to persist for the next several days. Meanwhile, a line of thunderstorms has remained active along a stationary front west of the state, sending high- level cirrus clouds streaming over the island chain. These high clouds are expected to linger through tonight and into tomorrow.
An area of deeper moisture can be seen upstream of the state on satellite this afternoon, and is forecast to move across the islands overnight into Friday. As this moisture arrives, an increase in windward and mauka showers is expected late tonight into Friday morning, even as trade winds gradually ease and veer slightly.
Looking ahead to the weekend, in addition to the moisture arriving on the trades, an axis of deep moisture will approach from the west as an upper-level trough swings overhead. The combination of increasing moisture and instability will bring the potential for localized flooding and isolated thunderstorms late Friday afternoon into Saturday, particularly across the western end of the state. Winds will be lighter during this period. While the overall pattern is somewhat complex and has posed forecast challenges, confidence is increasing that Kauai could see periods of moderate to locally heavy rainfall capable of producing localized flooding. As a result, a Flood Watch has been issued for Kauai County from 3 PM Friday through 6 AM Saturday.
Beyond the weekend, model guidance suggests that between Sunday night and Tuesday, moisture pooled along a horizontally-oriented frontal boundary will shift southward down the island chain as high pressure builds north of the state between two nearby lows. This boundary will bring another uptick in windward and mauka showers as it moves through, followed by strengthening trade winds. By the latter half of next week, mid-level ridging is expected to build overhead, supporting a more stable pattern with moderate to breezy trade winds.
Breezy trade winds will continue to weaken slightly through tomorrow as high pressure to the north weakens. Isolated to scattered showers, mainly windward, will be with us overnight and on Friday.
Brief MVFR due to visibility in showers was observed today and will remain possible in the strongest showers through tonight. However, the probability of occurrence is too low to put in the TAFs.
AIRMET Tango is in effect for tempo moderate turbulence below 8000 feet over leeward sides of the islands as a result of the strong low level winds. We also have light to moderate turbulence aloft between 26kft and 38kft. This AIRMET is expected to continue into the evening. However, conditions may become marginal as winds decrease late tonight.
A strong high pressure system to the north and a low pressure system and front just west of the offshore waters will allow strong to near gale force east to east southeast winds to persist through tonight. Winds have been on a slow downward trend from today and will continue to gradually decrease through Friday. Trade winds are expected to quickly weaken Friday night into Saturday as a broad trough develops near the state with light and variable winds expected over the weekend. Small Craft Advisory has been extended for all zones through tonight and has been scaled back to the windward zones and channels on Friday as the trades decrease below advisory threshold for several leeward waters on Friday.
Unsettled weather is expected Friday through the weekend as an upper level trough is forecast to move over the islands from west to east. Isolated thunderstorms can be expected around Kauai and Oahu waters by Friday afternoon, then spread to the rest of the islands by the weekend. Windward waters currently appear to have the highest chance of thunderstorms.
Nearshore buoys and surf observations continue to show advisory level surf along east facing shores with very little change among wave heights on the buoys. Thus the High Surf Advisory (HSA) has been extended through tonight. Surf should gradually ease tonight, and will likely be near the low end advisory threshold by Friday morning. The HSA may need to be extended through Friday, but surf heights should drop below advisory threshold by later in the day Friday.
Surf along north and west facing shores will remain well below seasonal levels through the weekend, and surf along south facing shores will remain small. Some trade wind swell will continue to wrap into select north and south facing exposures.
Forerunners from a large, long-period north to north-northeast swell are forecast to arrive Sunday night, then rapidly build to near warning levels along north facing shores Monday through Tuesday. Also due to the northerly direction, elevated surf heights are expected along west Maui and west Big Island near Kua Bay. Surf heights are expected to reach advisory threshold for west Big Island on Monday and could reach advisory threshold for west Maui as well. Lastly, due to the large swell and northerly direction (010-030 degrees), heavy surges are expected along north facing harbors such as Kahului and Hilo harbors.
Flood Watch from Friday afternoon through late Friday night for Niihau-Kauai-
High Surf Advisory until 6 AM HST Friday for Olomana-Maui Windward West-Kauai East-Kauai South-East Honolulu-Koolau Windward-Molokai Windward-Molokai Southeast-Windward Haleakala- Kipahulu-Big Island Southeast-Big Island East-Big Island North.
Small Craft Advisory until 6 PM HST Friday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Channel-Oahu Windward Waters- Kaiwi Channel-Maui County Windward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters.
Small Craft Advisory until 6 AM HST Friday for Kauai Leeward Waters-Oahu Leeward Waters-Maui County Leeward Waters.
