First Alert Forecast: Time to prepare is now, severe storm approaching

HONOLULU (HawaiiNewsNow) – If you liked the weather yesterday, you can pretty much copy and paste that onto today’s forecast. It’ll be another nice day with a mix of clouds and sunshine. However, this morning, unstable clouds are moving into the windward slopes of the islands, bringing showers to mountain areas.

That will change as a really strong low-pressure system moves toward the islands and strengthens as the week goes on, with tomorrow (Monday) being a transition day. This is a serious storm system for Hawaii that will start impacting us on Tuesday and last through the weekend, bringing heavy flooding, strong and gusty winds, thunderstorms that could become severe, and five days of winter weather for the summits and higher slopes of Mauna Kea and Mauna Loa.

A great tool to have is our First Alert Weather App and interactive radar.

Rain/Thunderstorms

Even though the storm center is hundreds of miles away, its effects are already being felt. Thunderstorm bands are forming 500 to 700 miles from the storm’s center, and high-level clouds with embedded thunderstorms are already showing up just 150 to 250 miles west of Kauai. A super-strong jet stream (a fast-moving air current) is pushing these storm bands toward Hawaii. A Flood Watch may be issued this afternoon.

Ensemble models are in good agreement on the track and intensity of this storm. The combination of tropical moisture moving north and the way the upper atmosphere is set up will create deep, organized thunderstorms that will bring heavy showers throughout the islands. The first few days of rain will completely soak the ground. Once the soil is saturated, even lighter rain will quickly turn into runoff and cause flooding. That means the flooding threat actually gets worse later in the week, not better. Heavy rain starting Tuesday will bring 4 to 12 inches of rainfall statewide over the next five days.

Wind

Starting Tuesday, winds will shift to blow from the south and southwest as the storm system approaches. These winds will get progressively stronger through the week. By Friday through Sunday, the winds will be dangerous — strong enough to knock down trees, especially on the northern and eastern slopes of the islands’ mountains. A High Wind Advisory or High Wind Warning is likely to be issued.

The heavy rain earlier in the week will soak the ground and weaken tree root systems. When the strong winds hit, these weakened trees will be more likely to fall. Falling trees and branches will likely knock down power lines, causing power outages across the state.

On top of the strong winds, severe thunderstorms will develop as tropical moisture and southerly winds collide. These storms could be dangerous, with:

• Damaging wind gusts
• Very heavy rainfall
• Dangerous lightning

A Severe Thunderstorm Watch may be issued at some point during this event.

High-elevation snow and ice, along with stronger winds, are also expected over the highest elevations of Mauna Kea and Mauna Loa on Hawaii Island. These conditions will likely limit road access to the observatories at summit level. Winter Storm Warnings are likely to be issued for those areas later this week.

Surf

Expect choppy conditions on east-facing shores today, then calmer surf for most of the week. North and west shores will see small, steady waves, while south-facing shores will turn rough and choppy starting Tuesday.

Get 10-minute weather updates, plus your 7-day forecast on Hawaii News Now Sunrise every weekday morning from 4:30 a.m. to 9 a.m. HST with Guy Hagi and team. Meteorologist Drew Davis will have your updates in the midday and early evenings and then Meteorologist Jennifer Robbins at 4 p.m. until 7 p.m; then at 9 p.m. and 10 p.m. on Hawaii News Now. Also on weekend mornings with Billy V & weekend nights with Ben Gutierrez.

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