Big Island Weather Forecast – What You Need to Know (ELI5 Edition)
TL;DR – A tropical storm named Moke is passing far south of Hawaii. It’s pulling in lots of moisture and making the trade winds stronger than usual. Expect heavy rain and possible flash flooding on the Big Island (especially windward and southeast slopes) through Monday, gusty winds up to 50 mph in some spots, and choppy seas. Conditions improve Tuesday as the storm moves away.
1. Quick‑Look at the Alerts ( Important!)
| Alert |
Where |
Until |
What it means for you |
| Wind Advisory |
Lanai, Maui, Molokai, Kohala, Big Island interior & many coastal zones |
Midnight tonight (HST) |
Winds 30‑50 mph with higher gusts. Secure loose items, avoid high‑profile vehicles, and stay off exposed ridges. |
| Flood Watch |
All of Big Island |
Monday afternoon |
Heavy rain could cause flash flooding. Keep an eye on road closures, avoid crossing streams, and have an evacuation plan if you live in a low‑lying area. |
| Small Craft Advisory |
All Hawaiian waters |
6 AM HST Monday |
Seas are rough (6‑10 ft) and winds are strong. Small boats should stay in port; larger vessels should use caution. |
| Tropical Storm Warning (Offshore) |
Offshore waters south of the islands |
Until Moke exits (by Monday) |
Storm‑force winds & heavy rain over open water. Not a direct threat to land, but it’s why the winds are so strong. |
Callout: If you’re on the Big Island, treat Monday as a “stay‑indoors‑if‑possible” day. Flooding can happen fast on steep slopes.
2. Forecast by Region (What “Tonight”, “Monday”, “Monday Night” Mean)
ELI5: Think of the day split into three chunks: “Rest of Tonight” (the next few hours), “Monday” (daytime), and “Monday Night” (evening into early Tuesday).
Below each region you’ll see the high/low temperatures, wind, and rain chance. All temperatures are in °F.
Hilo (Windward, low‑elevation)
| Period |
Weather |
Temp (Low‑High) |
Wind |
Rain Chance |
| Rest of Tonight |
Showers (steady) |
70‑76 °F (shore) • 63 °F (4 000 ft) |
West ≤10 mph |
≈100 % |
| Monday |
Morning showers → numerous afternoon showers |
81‑87 °F (shore) • 69 °F (4 000 ft) |
East ≤15 mph (increasing) |
≈100 % |
| Monday Night |
Mostly cloudy, scattered showers |
67‑75 °F (shore) • 60 °F (4 000 ft) |
NE ≤10 mph |
50 % |
Kona (Leeward, low‑elevation)
| Period |
Weather |
Temp (Low‑High) |
Wind |
Rain Chance |
| Rest of Tonight |
Partly cloudy, early showers then isolated |
71‑77 °F (shore) • 61 °F (5 000 ft) |
Light |
50 % |
| Monday |
Mostly sunny morning → mostly cloudy afternoon with numerous showers |
~89 °F (shore) • 73 °F (5 000 ft) |
Light |
70 % |
| Monday Night |
Mostly cloudy evening showers → partly cloudy, isolated after midnight |
74‑79 °F (shore) • 53‑59 °F (5 000 ft) |
Light |
50 % |
Waimea & Kohala (Higher terrain, breezy)
Both zones share the same forecast because they sit on the same wind‑exposed slopes.
| Period |
Weather |
Temp (Low‑High) |
Wind |
Rain Chance |
| Rest of Tonight |
Mostly cloudy, breezy, showers early → numerous after midnight |
70‑76 °F (shore) • 64‑70 °F (3 000 ft) |
East ≤25 mph |
90 % |
| Monday |
Mostly cloudy, breezy, numerous morning showers → scattered afternoon |
~83 °F (shore) • 72‑82 °F (3 000 ft) |
East ≤25 mph |
70 % |
| Monday Night |
Mostly cloudy → partly cloudy, breezy, scattered showers |
66‑75 °F (shore) • 59‑65 °F (3 000 ft) |
East ≤20 mph |
40 % |
South Big Island (Very windy, high rain)
| Period |
Weather |
Temp (Low‑High) |
Wind |
Rain Chance |
| Rest of Tonight |
Windy + showers |
~78 °F (shore) • 63 °F (5 000 ft) |
East 10‑30 mph, gusts 50 mph |
≈100 % |
| Monday |
Windy, partly sunny, scattered showers |
~88 °F (shore) • 72 °F (5 000 ft) |
East 10‑30 mph |
50 % |
| Monday Night |
Partly cloudy, breezy, evening showers → isolated after midnight |
~75 °F (shore) • 56 °F (5 000 ft) |
NE ≤25 mph |
40 % |
Puna (Similar to Hilo)
| Period |
Weather |
Temp (Low‑High) |
Wind |
Rain Chance |
| Rest of Tonight |
Showers |
70‑76 °F (shore) • 63 °F (4 000 ft) |
West ≤10 mph |
≈100 % |
| Monday |
Morning showers → numerous afternoon |
81‑87 °F (shore) • 69 °F (4 000 ft) |
East ≤15 mph (increasing) |
≈100 % |
| Monday Night |
Mostly cloudy, scattered showers |
67‑75 °F (shore) • 60 °F (4 000 ft) |
NE ≤10 mph |
50 % |
Waikoloa (Leeward, a bit higher)
| Period |
Weather |
Temp (Low‑High) |
Wind |
Rain Chance |
| Rest of Tonight |
Partly cloudy, breezy, early showers → isolated after midnight |
73‑78 °F (shore) • 62 °F (4 000 ft) |
East ≤20 mph |
50 % |
| Monday |
Partly sunny, scattered showers |
86‑92 °F (shore) • 69‑76 °F (4 000 ft) |
North ≤15 mph |
50 % |
| Monday Night |
Breezy, evening showers → partly cloudy, isolated after midnight |
~77 °F (shore) • 54‑61 °F (4 000 ft) |
East ≤20 mph |
40 % |
3. Big‑Picture Synopsis (What’s Happening & Why)
- Tropical Storm Moke is ~300 mi south‑southwest of Kona, moving west.
- Its outer moisture band is brushing the southern tip of the Big Island, dumping rain on windward & southeast slopes.
- The storm’s pressure gradient (difference in air pressure) is tightening the trade winds across the whole state → gusts up to 50 mph on exposed ridges.
- Rainfall on the Big Island has been light‑to‑moderate so far (<1 in in 12 hrs), but the window for heavy rain & flash flooding is through early Monday morning on windward sides, with a secondary chance of localized flooding in Kona districts Monday afternoon.
- Tuesday onward: Moke moves away → trade winds relax to moderate, moisture drops → typical trade‑wind weather (showers mainly on windward slopes).
4. Technical Details (Simplified for Everyone)
| Topic |
What it means (ELI5) |
| MVFR / IFR |
Aviation codes: MVFR = “Marginal Visual Flight Rules” (visibility a bit low, pilots need instruments sometimes). IFR = “Instrument Flight Rules” (visibility poor, pilots must fly by instruments). |
| AIRMET Tango |
Advisory for low‑level turbulence behind mountains caused by strong trades. |
| AIRMET Sierra |
Advisory for mountain obscuration (clouds/fog hiding peaks) on windward sides. |
| TC SIGMET XRAY |
Special weather bulletin for tropical cyclone (Moke) convection – tells pilots where thunderstorms are. |
| Orographic lift |
When moist air hits a mountain, it’s forced up, cools, and drops rain. That’s why windward slopes get soaked. |
| Trade winds |
Steady east‑to‑northeast breezes that normally blow across Hawaii. They’re stronger now because Moke’s low pressure pulls them tighter. |
5. Aviation & Marine Impacts (If You Fly or Boat)
Aviation
- Windward Big Island: Expect MVFR/IFR conditions tonight → possible delays or diversions.
- Elsewhere: Mostly VFR (good visibility) with occasional MVFR in passing showers.
- Turbulence & mountain obscuration advisories active → pilots should plan extra altitude or alternate routes.
Marine
- All waters: Fresh to strong winds (20‑30 kt, gusts higher) through tonight.
- Small Craft Advisory until 6 AM Monday → small boats stay in harbor.
- Seas: 6‑10 ft, choppy, especially east‑ and southeast‑facing shores.
- Surf: East‑facing shores will stay elevated & choppy Monday; south‑facing shores near summer norm but a small south‑swell (3‑4 ft) arrives Mon‑Tue.
6. Fire Weather Outlook
- Winds: Strong now, easing tonight & Monday.
- Humidity: Higher than usual because of Moke’s moisture → lower fire danger today.
- Rain: Heavy on windward/SE Big Island; lighter elsewhere.
- Tuesday: Return to normal summer trade‑wind pattern → fire risk back to typical levels.
7. Step‑by‑Step: What Should You Do Right Now? (Numbered Checklist)
- Check local road & trail closures (especially near streams, gulches, and low‑lying roads).
- Secure outdoor items (trash cans, patio furniture, tarps) – winds can turn them into projectiles.
- If you live in a flood‑prone area (near rivers, coastal lowlands), prepare an evacuation kit (water, meds, important docs).
- Avoid unnecessary travel on the Big Island Monday morning – flash floods can appear with little warning.
- Boaters: Stay in port or seek protected anchorage until Small Craft Advisory lifts.
- Pilots: Review NOTAMs for MVFR/IFR, AIRMETs, and SIGMETs; file alternate airports.
- Stay informed – monitor NOAA Weather Radio, National Weather Service Honolulu (@NWSHonolulu), or the Big Island Now website for updates.
8. Summary (One‑Paragraph Recap)
Tropical Storm Moke, though far south, is tightening the pressure gradient over Hawaii, producing gusty trade winds (up to 50 mph) and pulling a moisture plume over the Big Island. This brings near‑certain heavy rain and a Flood Watch for windward and southeast slopes through Monday, with scattered showers elsewhere. Wind Advisories and a Small Craft Advisory are active. Conditions improve Tuesday as Moke departs, returning to normal trade‑wind weather.
9. FAQ (Your Top Questions Answered)
| # |
Question |
Answer (ELI5) |
| 1 |
What is a “Flood Watch” vs. a “Flood Warning”? |
A Watch means conditions are right for flooding – be ready. A Warning means flooding is happening or imminent – take action now. |
| 2 |
Why are the winds so strong if the storm is 300 mi away? |
The storm’s low pressure creates a tight pressure gradient across the islands. Air rushes from high pressure (north) to low pressure (south), speeding up the normal trade winds. |
| 3 |
Should I cancel my hike on Mauna Kea or Mauna Loa Monday? |
Yes. High winds, low visibility, and possible flash flooding on trails make it unsafe. Check the Hawaii Volcanoes National Park alerts before going. |
| 4 |
What does “MVFR” mean for my flight? |
It means visibility is 3‑5 miles and/or ceilings 1,000‑3,000 ft – you can still fly visually but may need instruments. Airlines usually handle it, but small planes may delay. |
| 5 |
When will the Small Craft Advisory end? |
It expires 6 AM HST Monday for all waters, but local conditions (especially east‑facing shores) may stay choppy a bit longer. |
Final Tip: Weather can change fast on an island. Keep a phone alert on, tell a friend your plans, and respect the advisories – they’re there to keep you safe.
Data courtesy of NOAA / National Weather Service Honolulu. Forecast provided by Big Island Now (Blue Hawaiian Helicopters sponsor).