🌊 Conditions Guide

Understanding the physical environment at Kanaha Beach Park — how trade winds, thermal effects, tides, and swell interact to create the conditions you'll ride in.

Wind Regimes

Kanaha wind is a combination of synoptic trade winds and local thermal effects. The regime classification determines equipment selection and session quality.

Regime	Trade kts	Thermal	Result at Kanaha	Session Quality
Calm	<5	Weak	<10 kts — not rideable	No session
Pure Sea Breeze	<8	Strong	12-15 kts — thermal only	Marginal — big kite needed
Light Trades	8-12	Active	14-18 kts — gentle + boosted	Good — light wind foiling
Trades + Thermal	12-18	Active	15-22 kts — sweet spot ★	Excellent
Trades Dominant	18-25	Minor	20-28 kts — powered up	Strong — small kite, fast foil
Trades Overpowering	25+	Irrelevant	28+ kts — survival	Challenging — 2.2m + short lines

★ "Trades + Thermal" (15-22 kts NE) is the most common and most enjoyable Kanaha condition — good power, manageable gusts, organized windswell for bump riding.

Maui Isthmus Thermal Effect

The Maui isthmus — the low, flat valley between Haleakala and the West Maui Mountains — is the engine that drives Kanaha's wind. Understanding it is the key to predicting afternoon conditions.

How It Works

Solar heating — The isthmus heats up faster than the surrounding ocean, creating a low-pressure zone over the valley
Sea breeze — Cool ocean air is drawn into the low pressure, creating an onshore flow that adds to existing trade winds
Venturi compression — The wind accelerates as it's compressed through the gap between the two mountains, focusing energy at Kanaha

Diurnal Pattern

Time (HST)	Phase	Description
6:00–10:00	Build-up	Isthmus warming, thermal starting to develop
11:00–14:00	Peak	Maximum solar heating — strongest thermal boost
14:00–19:00	Decay	Linear decline as isthmus cools
19:00+	Evening	Thermal gone — only synoptic wind remains

⚡ #1 uncertainty: cloud cover. Clouds are the single biggest prediction variable. Overcast skies shut down solar heating of the isthmus, killing the thermal effect entirely. An expected 18 kt afternoon becomes 12 kts under clouds. The Open-Meteo per-hour cloud forecast is the most critical data field for accuracy.

Kanaha Bathymetry

Kanaha's reef creates both opportunity (wave breaking for surf) and hazard (mast/foil strike). Understanding the depth profile is essential for safe equipment selection.

Shore to Old Mans Reef

Old Mans reef sits approximately 200-300m offshore at Kanaha. At mean lower low water (MLLW), the reef is approximately 0.9m deep. Tides add to this baseline:

reef_depth = 0.9m + (tide_ft × 0.3048)

Mast Selection Logic

Reef Depth	Safe Mast	Logic
<95 cm	72 cm	Low tide — shortest mast for reef protection
95–105 cm	85 cm	Standard depth — default freeride mast
105–115 cm	90 cm	High tide — more stability and performance
>115 cm	100 cm	Very high tide — maximum performance

The 15cm clearance margin accounts for wave troughs and the dynamic dip of the foil during turns. The forecast system computes the minimum reef depth during the session window to select a safe mast.

⚠️ Reef strike hazard: Hitting the reef with a carbon mast at speed can snap the mast, damage the foil, and injure the rider. The 72cm mast exists specifically for low-tide protection. Never ride a 100cm mast at low tide over Old Mans reef.

Wave Types

Two fundamentally different wave types arrive at Kanaha, each created by different mechanisms and requiring different riding approaches.

Windswell (3–8 second period)

Source: Generated locally by trade winds blowing across the ocean surface
Direction: NE (aligned with trades)
Character: Short, choppy, closely spaced — "bumps" rather than "waves"
Best for: Downwind foiling — riding bumps with wind power

ℹ️ NE fetch advantage: When the trade wind blows from the NE, the fetch along Maui's north shore is maximized. This produces longer, more organized bumps — the ideal conditions for downwind foil gliding. Wind from other directions produces shorter, messier chop.

Groundswell (10–20 second period)

Source: Distant North Pacific storms (1,500–3,000+ nm away)
Direction: NNW to NW (north shore exposure)
Character: Long, powerful, widely spaced — true ocean waves
Best for: Wave riding — carving on open faces

Why It Matters for Foiling

Windswell bumps and groundswell waves are completely different riding experiences:

Windswell → downwind foiling with kite power, riding bump energy for glide
Groundswell → wave foiling on open faces, riding wave energy directly
Big groundswell makes the freeride zone unsafe (overhead breaking waves over the reef). The forecast system triggers a board switch to the low-volume duck-dive board when groundswell exceeds safety thresholds.

Swell Alert Levels

The system classifies incoming swell into 5 levels, each with specific implications for session planning.

Level	Height	Period	Meaning	Action
Flat	<0.5m	—	No significant swell	Normal freeride session
Small	0.5–1.0m	<12s	Minor swell, small surf	Normal session, fun bonus waves
Fun	1.0–2.0m	12–14s	Good wave riding	Wave foiling option, watch reef
Pumping	≥2m	14s+	Overhead+ surf	CANCEL PLANS — wave event
XXL	≥3m	16s+	Dangerous outer reef	Expert only — extreme caution

⚡ CANCEL PLANS flag: At "pumping" level and above, the forecast issues a WAVE-EVENT verdict. Overhead+ swell at Kanaha is rare (maybe 10-15 times per winter) and demands a completely different setup: wave board, wave foil, and full commitment. The system overrides normal session planning to highlight these events.

Session Windows

Session windows are set by day of the week, based on the rider's schedule constraints.

Day	Window	Duration
Monday–Thursday	12:00–4:00 PM	4 hours
Friday	12:00–5:00 PM	5 hours
Saturday	11:00 AM–5:00 PM	6 hours
Sunday	11:00 AM–4:00 PM	5 hours

The forecast system generates equipment recommendations and condition predictions for each 2-hour block within the window. Earlier blocks often have different gear than later blocks as thermal wind builds through the afternoon.

North Pacific Storm Tracks

Groundswell reaching Kanaha originates from storms in the North Pacific, typically between 1,500 and 4,000+ nautical miles away. The system monitors 5 zones for storm generation.

Monitored Zones

Zone	Coordinates	Typical Travel Time	Notes
Gulf of Alaska	56°N / -148°	2–4 days	Most common source, NW swell direction
Mid-Pacific	40°N / -155°	1.5–3 days	Closer source, quicker arrival
Western Pacific	47°N / -175°	3–5 days	Produces WNW swell angle
Central North	50°N / -160°	2.5–4 days	Clean NNW swell direction
Far West	45°N / 175°	4–6 days	Long-distance, high-period swell

Why Longer Period = Faster Travel + More Predictable

Swell energy travels at group velocity, which is directly proportional to wave period:

Cg = g × T / (4π)   m/s

This means:

A 16-second swell travels at ~12.5 m/s (24 kts) — arrives quickly
An 8-second swell travels at ~6.2 m/s (12 kts) — takes twice as long
Longer period also means the swell has traveled farther, which means it's more organized (short-period chop has already dissipated)

ℹ️ Early warning system: The North Pacific monitoring buoys (46001, 46035, 46066) and Open-Meteo marine waypoints give 2–6 days of advance notice before swell arrives at Maui. Combined with NDBC buoy 51001 (NW Hawaii) as the final "doorbell" ~12-18 hours before arrival, the system provides reliable early warning for significant swell events.