CAPE-Driven Secondary Thermals – When Afternoon Convection Adds 5–7 Knots
You check the forecast: 12 knots. You arrive at the beach, and massive puffy clouds are forming inland. Suddenly, the wind speed spikes to 18 knots. You just felt a CAPE boost.
CAPE (Convective Available Potential Energy) measures the instability of the atmosphere. While usually used to predict thunderstorms, for wingfoilers, moderate CAPE values indicate "Secondary Thermals" that enhance the sea breeze.
The Mechanism
A standard sea breeze is a 2D flow: air moves from sea to land. When CAPE is high (>500 J/kg), the land air rises explosively. This creates "Cloud Streets" or "Horizontal Convective Rolls".
These rolling cylinders of air align with the wind. Under the sinking branch of the roll, the wind speed is compressed and accelerated. This adds a "gust factor" of 5–7 knots on top of the base forecast.
The "White Puffy" Indicator
Look inland.
- Flat Blue Sky: Low CAPE. Steady but potentially weak wind.
- Towering Cumulus: High CAPE. The atmosphere is sucking air off the ocean. Expect strong wind gusts and a boosted average speed.
If the clouds get too big (Anvil tops), the CAPE is too high (>1500 J/kg). This creates thunderstorms, which kill the steady wind and replace it with dangerous squalls.
Timing the Surge
CAPE-driven wind usually peaks later than a standard thermal.
- 1 PM: Standard sea breeze starts.
- 3 PM: Convection peaks. The clouds form. The wind speed jumps.
- 5 PM: As the sun lowers, the convection dies, and the wind drops back to the base level.
Using the Model
Check the ICON or GFS model for the "CAPE" parameter.
- 0 J/kg: Stable. What you see is what you get.
- 200–800 J/kg: The Sweet Spot. Expect a 5–7 knot bonus.
- >1000 J/kg: Danger zone. Watch for lightning.
Summary
If the wind forecast looks borderline (10–12 knots) but the CAPE map shows moderate instability, go to the beach. The convective engine will likely kick in, turning a light wind day into a powered 15–25 knots session.