1. Chapter 15
Weather and Boating

2. Lesson Objectives Weather information sources Basic storm patterns
Storm forecasting and precautions
Go/no go decision making
Personal weather equipment and equipment check list
SSSpptChpt15Weather ppt

3. Weather Information Sources of weather information: NOAA
Private wx services
Intellicast, etc.
USCG Broadcasts
Local sources
Personal observation
SSSpptChpt15Weather ppt
Courtesy of NOAA

4. Wind and Boating What can happen to a vessel caught in a storm?
SSSpptChpt15Weather ppt
Courtesy of FEMA

5. Winds and Boating Storm surge Swells Breaking waves
Wave height and period
Waves in shallow water
Seamanship vs. seaworthyness
SSSpptChpt15Weather ppt

6. Ripples without foam crests.
Winds and Boating
Table 12-1
Beaufort Wind Scale
Beaufort Number
Wind Description
Mean Wind Speed Equivalent (knots)
Mean Wave Height
Sea Conditions
meters feet
Seas tumultuous. The air is filled with foam. The ocean is totally white with driving spray. Visibility seriously reduced.
64 +
Hurricane 12
High waves; crests begin to tumbler; dense streaks of form. Spray affects visibility.
41-47
Strong gale 9
moderate waves with a more pronounced long form; many whitecaps. A little spray.
17-21
Fresh breeze 5
Ripples without foam crests.
1-3
Light air 1
Sea is like a mirror.
≤ 1
Calm
SSSpptChpt15Weather ppt
Copyright Hal Roth, 2006 Reprinted with permission

7. Understanding Weather
Sea breeze
Daytime: Land warms, warm air rises, cooler sea air flows in
Land breeze
Nighttime: Land cools, cool dense air flows out to sea
SSSpptChpt15Weather ppt
Reprinted with permission from Gary Jobson’s Championship Sailing by Gary Jobson

8. Understanding Weather
Coriolis Force
Causes rotation of pressure systems
SSSpptChpt15Weather ppt

9. Understanding Weather
Temperature and humidity
Moisture and energy
Air masses
High pressure system
Low pressure system
SSSpptChpt15Weather ppt

10. Understanding Weather
Low pressure systems
High pressure systems
SSSpptChpt15Weather ppt
Adopted from Boater’s Bowditch by Richard K. Hubbard

11. Understanding Weather
Why do we have inclement weather with a low pressure system?
Cold, dense air mass flows under warm, moist air mass
Warm, moist air rises, cools, and water vapor condenses into precipitation
Closing isobars mean increasing winds, as air flows from high to low pressure area
Rapid vertical development: thunderstorms
SSSpptChpt15Weather ppt

12. Understanding Weather
Buys Ballot’s Law
SSSpptChpt15Weather ppt

13. Understanding Weather
Symbols: Fronts
Warm front: Leading edge of warm air mass
Cold front: Leading edge of cold air mass
Occluded front: Cold air mass underlying warm air mass
warm front
cold front
occluded front
SSSpptChpt15Weather ppt

14. Understanding Weather
Clouds and Fronts
What are the three types of clouds and characteristics of each that accompany fronts?
SSSpptChpt15Weather ppt

15. Understanding Weather
High, mid-level, and low clouds
Cirrus: (high): “locks of hair”
Cumulus: (low-, mid-level) “pile or accumulation”
Stratus: (low-, mid-, high-level) “solid layer”
Alto: (mid- to high-level) “high, upper”
Nimbus: low-, mid-level “rainy”
Typical types: Cumulonimbus, cirrostratus, altocumulus, cumulus, etc.
Generally avoid: Cumulonimbus, cumulus
SSSpptChpt15Weather ppt

16. Understanding Weather
Approaching a low
Approaching a warm front
Passing warm front
Within warm sector
Approaching cold front
Passing cold front
SSSpptChpt15Weather ppt

17. Understanding Weather
Fog: a cloud touching the earth
Radiation fog: Land-based, caused by surface cooling and subsequent condensation
Advection fog: Warm, moist air flows over cooler surface, causing condensation
Haze: Dust or salt particles in the air
Mist: Particles of liquid water in the air
Smog: Fog and smoke mixed
SSSpptChpt15Weather ppt

18. Fog Precautions What precautions must be taken in fog?
Navigate, Communicate, Mitigate
Navigate: (avoid danger)
Communicate: (with proper fog signal)
Mitigate: (slow down)
Look and listen
SSSpptChpt15Weather ppt

19. Non-Frontal Weather Thunderstorms! Single-cell Multicell cluster
From least to most dangerous:
Single-cell
Multicell cluster
Multicell lines 
Supercell
SSSpptChpt15Weather ppt

20. Thunderstorms Waterspouts Tornadoes Microbursts Lightening
SSSpptChpt15Weather ppt
Courtesy of NOAA

21. Non-Frontal Weather In sight of a thunderstorm? If you cannot avoid:
Determine its path and steer to avoid if possible
Get a weather report, check radar picture
If you cannot avoid:
Prepare for heavy weather
Reduce sail
Close hatches and secure loose gear
Put on foul weather clothing, life jackets, tethers
SSSpptChpt15Weather ppt
Courtesy of NOAA

22. Non-Frontal Weather Tropical Storms Tropical wave Tropical cyclone
Circulation begins with wave in isobars
Tropical cyclone
Closed isobars, winds <64 knots
Hurricanes
Intense circulation, winds >64 knots
SSSpptChpt15Weather ppt
Courtesy of NOAA

23. The Go/No-Go Decision Making Go/No Go decision: Vessel seaworthiness
Crew experience
Weather forecast
Wind direction and speed, temperature, precipitation, waves
Purpose and length of voyage
Crossing a harbor or an ocean?
SSSpptChpt15Weather ppt
Courtesy of NOAA