- > Decreasing barometric pressure indicates storms, rain, and windy weather.
- > Rising barometric pressure indicates good, dry, and colder weather.
- > A slow, regular, and moderate fall in pressure indicates a low-pressure area is passing in a nearby region. Marked changes in the weather where you are located are unlikely.
- > A small, rapid decrease in pressure indicates a change in weather near you, usually followed by a brief spell of wind and showers.
- > A quick drop in pressure over a short time means you can expect a storm in five to six hours.
- > A large, slow, and sustained decrease in pressure is a precursor to a long period of poor weather. This weather will be more severe if the pressure had been rising before it began to drop.
- > A rapid rise in pressure during fair weather and average or above-average pressure means a low-pressure cell is approaching. The pressure will soon decrease, forecasting poorer weather.
- > When low pressure quickly rises, a short period of fair weather is likely.
- > A large, slow, and sustained rise in pressure means a long period of good weather is on its way.
CONSULT RADAR I realize every one of you may not have installed a radar system, but if you have radar, use it. While a radar system’s main function is to spot obstacles and report their position relative to a fixed object (your boat) via a blip on the radar screen, a side benefit is you can use it to spot masses of precipitation and track their progress. Radar (radio detecting and ranging) transmits microwaves in a focused beam. Some of this microwave energy bounces off objects and returns to the radar to be measured. The radar sends pulses of energy, rather than a continuous signal, and it measures how far away an object was when the microwaves reflected off it. Combined with the radar’s ability to scan up, down, and in a circle in all directions, modern radars can measure the three-dimensional distribution of precipitation within 100 miles of the radar. Precipitation shows up as a blob, which is colored differently (ours is blue) than land masses and the like. Once you notice precipitation headed your way, you can evade it by delaying departure or changing course, or you can prepare to deal with it.
It’s common for us to sense changes in the weather. You may look at the clouds, the color of the sky, feel a change in the wind or humidity, and intuitively know what to expect. But sometimes, nature gives us tangible clues.
UNDERSTAND THE SKIES Clouds are formed from water that evaporates from oceans, lakes, and rivers. When warm, moist air rises, it expands and cools, creating humidity. The presence of high, puffy clouds usually means the air is dry and air pressure is high. Horizontal, flat clouds are a sign of rain. Lowering clouds means moisture is collecting and it may rain, whereas rising clouds signify clearing. The darker the cloud, the greater the chance of rain. Clouds that appear clumpy and wispy, like fish scales (mackerel sky) or a horse’s tail (mare’s tail) often precede a storm. The adage is true: Red sky at night, sailors’ delight. Red sky in morning, sailors take warning. The red color is caused by light refracting off dust particles in the air, which indicates a lack of moisture. When the sun goes down in the west, turning the sky red, dry weather is approaching. A red sky at sunrise means dry weather has moved away and moisture is in the air. If the sky is gray to the west, it means rain is coming; to the east, it has likely passed. Is there a rainbow? If the wind is coming from the direction of the rainbow, the rain is heading toward you. Conversely, if the rainbow is in the opposite direction, it has passed you. When the sun is in the east in the morning, and the shower and asso- ciated rainbow are in the west, it’s going to rain. A halo around the moon or sun is caused by high cirrostratus (ice crystal) clouds that signal the approach of a warm front and is a sign that rain will fall within twen- ty to twenty-four hours. The US Weather Service confirms that rain follows about 75 percent of sun halos and about 65 percent of moon halos.
NOTE WIND SHIFTS Change in wind strength and direction is easy to determine because you can actually feel it. Your hair will blow wildly about or lay flat, and your skin may sting from it. Anything that flaps, such as the flag on the stern of your boat or the telltales (strips of yarn or ribbon) on a sail, will give you clues about the direction and strength of the wind. If you have one installed, a wind gauge or a wind direction finder will verify what you may already know. When you tune into the weather channel on your VHF radio or other such device, you may hear mention of the Beaufort scale. Devised back in the 1800s, this scale was originally used to gauge the effects of wind on ships at sea. The Beaufort scale classifies wind from Force 0 (calm, at less than 1 mph) to Force 12 (hurricane, at 74 mph or greater). Categories 1 through 11 include light air, five levels of breeze, four levels of gale, and storm-force winds. Wind is air in motion moving horizontally at any velocity along the earth’s surface. It is created when warm air expands, becoming less dense (thus lighter), and rises, and then is replaced by colder, denser (heavier) air. These differences in temperature create local breezes and global winds. The larger the area, the more heat or cold air it will hold and sustain. Coastal cities near the ocean are warmer or cooler than those inland, depending on the season and time of day.
CHECK THE WATER
Choppy white water indicates a rapid shift or increase in the prevailing wind condition. An increasing swell plus advancing storm clouds mean an approaching low with a large area of strong winds.
While heavy rain can certainly deteriorate visibility, nearly anywhere there is a temperature difference between the air and the water, rain is often combined with fog, often referred to as pea soup. If you live in the northeast United States, like I do, you know what fog is. Fog can occur almost any time of year on lakes and rivers, as well as on oceans. Due to great differences in water and air temperatures, you won’t see much of it in the south or the tropics, but you will be plagued with it in northernmost areas. It also occurs in places where humidity in the air is high enough to form condensation. When you listen to the weather channel on your VHF radio, NOAA will state the visibility in certain areas. For example, 100-foot visibility means if another boat is 100 feet from you, you will not see it. You will hear descriptions like “dense fog” or “patchy fog.” They may predict the fog will burn off or remain for a certain period of time (as when accompanied by a low-pressure system), as well as the areas fog is located. Use this information to rethink your destination or the course to your destination, plan your departure time, or reschedule your cruise. If you are in port and can’t see past the end of the dock, I highly recommend delay- ing or canceling departure until the fog lifts. Fog can vary from a light haze due to humidity in the air, to a total whiteout-type situation. Not only will fog impact visi- bility, but it will muffle sound and magnify obstacles. The denser the fog, the lower your chances of detecting the presence of another boat, a buoy, or a land mass. It’s as if the sky dropped a white sheet over every- thing, except the small circle of water surrounding you and your boat. Although you may feel alone, you’re probably not. When a buoy or another boat looms up in front of you, seemingly out of nowhere, it’s scary.
NAVIGATE IN FOG
No one wants to encounter fog, but there are situations where it can’t be avoided. Navigating in fog requires sharp eyes and quick reflexes. If you are underway and fog rolls in or you run into an area of fog, follow these ten steps:
- 1. Reduce your speed.
- 2. Turn on your navigation lights to increase your boat’s visibility to other boats.
- 3. If you have radar, monitor it for the presence of other boats or obstacles, and track any movement that could result in a collision.
- 4. Assign a crew member with sharp eyesight to keep watch.
- 5. Stay at the helm. Steer manually and be prepared to switch direction if an unexpected boat or object looms up out of the fog.
- 6. Keep to a course using each marker to verify your exact position relative to your destination.
- 7. Compare the designated water depth on your navigation chart with your actual depth as shown on your instruments to verify your location as you move along. If you are in 12 feet of water when the chart states you should be in 50 feet, you are way off course.
- 8. Sound an air horn or the horn on your boat at regular intervals to alert others to your presence.
- 9. Pray the fog lifts soon.
HOW WEATHER FRONTS CAUSE CHANGE
Weather changes begin with what we call a front, which is the boundary between a cold and a warm air mass. The air masses do not mix but move with respect to each other, resulting in a change of weather conditions at a particular location. Fronts can be warm or cold, but in either case they mean a weather change is on the way. As a rule, warm fronts bring good weather, whereas cold fronts signal rain. Some parts of the country, like the northeast United States, can experience several weather changes in a single day. You may encounter one of these types of fronts: Cold front: An oncoming cold air mass pushes under a warm air mass and forces it upward. This causes a drop in barometric pressure and signals a line of approaching rain. Cold fronts generally move from northwest to southeast. The air behind a cold front is colder and drier than the air ahead of it. Warm front: A warm air mass approaches and overrides a cold air mass. Light rain, snow, or sleet (depending on the climate) may occur before and as the front passes. Behind the front, expect clearing skies and warmer temperatures. Stationary front: This occurs when a front slows down with little or no forward movement. Once it resumes motion as a warm or cold front, expect a temper- ature change or a wind shift as it crosses from one side of a stationary front to the other. Occluded front: This kind of front may be warm or cold. In either case, the front has defined vertical boundaries between the coldest air, the cool air, and the warm air, which results in air pressure changes and winds typical of storms. In most cases, storms begin to weaken after a frontal occlusion occurs.
COPE WITH STORMS
There are various types of storms, and none of them are fun to be caught in while on cruise. Sure, a passing rain shower may be uncomfortable, and you may get wet, but it isn’t threatening until the winds pipe up, thunder rolls, and bolts of lightning streak from the sky. Thunderstorms are common in tropical areas or during summertime, when the air is warm and humid. The radiant heat from the land absorbs moisture from nearby water and rises to produce thunderheads. A cold front may be preceded by squall lines, or a row of black storm clouds. Wind shifts unpredictably and accelerates.
- lightning arrester = a device used in preventing damage to radio, telephone, or other electrical equipment.
- lightning rod = a rodlike metal conductor installed to divert lightning away from a structure by providing a direct path to the ground.
- surge protector = a small device to protect a computer, telephone, or other electrical device from damage by high-voltage electrical surges.
WHAT TO DO IN A LIGHTNING STORM
If the sky is alight with jagged bolts, protect yourselves and your boat as best you can until the storm is over. Keep within a protected area in the center of the cabin or low in the boat, depending on the design of your boat. If your hair stands on end and your body tingles, lie flat on the floor. This is the first warning of a strike or flash. Don’t dangle arms and legs in the water. Disconnect and then do not touch or use major electronic equipment, including the radio, throughout the storm. Avoid making simultaneous contact with any two components of any portion of the boat that are connected to the lightning protec- tion system. If your boat has been hit by lightning, or you suspect it has, the extent of any dam- age caused may not be obvious. Once you have checked the electrical system and compasses, consider having the boat hauled to have the hull inspected to be sure the point at which the lightning exited is not cracked or damaged in any way. Even a tiny crack can create a leak that could ultimately sink your boat. If a crewmember is struck and disabled, call for assistance using your VHF radio. Know that there is no danger in touching a person who has been struck by light- ning. Increase his or her chances of survival with immediate medical care, artificial respiration, or CPR.
HOW TO HANDLE A RAINSTORM
It’s Sunday and you need to cruise home because you have to work tomorrow, the kids have school, and your spouse has a dentist appointment. It’s raining and the sky looks black; NOAA predicts the weather will deteriorate as the day progresses. You make a decision to leave early to miss the worst of it. Heck, in two hours, you could be in the car driving home. So you head out. The seas are rougher than you expected, but you push on anyway. As you progress, the weather worsens, but you are an hour from home and it’s too late to turn back.
- 1. Point your bow to the wind.
- 2. Take waves at a 40- to 45-degree angle.
- 3. Don personal flotation devices (PFDs).
- 4. Close all hatches and ports.
- 5. Secure any loose items that could be tossed about.
- 6. If lightning is expected, lower or remove and tie down the radio antennas and any protruding devices not part of the lightning protection system of your boat.
A squall is a burst of violent weather accompanied by intense winds. Many kinds of squalls occur over various places on Earth. Some are the result of unique local conditions and do not occur elsewhere; others emerge from normal weather processes. You may encounter these basic types of squalls:
- Rain squall: This is usually part of a line of thunderstorms forming along or in advance of a cold front. The winds increase quickly, churning up the waters and usually bringing heavy rain. A squall may last ten minutes or half an hour but should be taken as a warning sign that more such weather is on the way.
- White squall: You may have heard the term white squall or read about one in an old sea story. The name refers to the color of the waves caused by a sud- den increase in wind velocity in tropical and subtropical waters. White squalls are common on the Great Lakes of North America. This kind of storm sneaks up on you because there are no black clouds, typical of rain squalls, to warn you of its approach. Some say a white squall and a microburst are the same.
- Microburst: This is a sudden and intense downdraft within a severe thunder- storm that produces powerful winds. Unlike a tornado, the winds in a mi- croburst travel downward and outward and do not rotate. It lasts between five and fifteen minutes with winds of more than 100 mph causing significant damage.
WHAT TO DO IN A SQUALL
When the wind shifts 180 degrees and wind speed builds from a pleasant breeze to chilling proportions, you are likely going to be slammed with a squall. This hap- pens so quickly that there often isn’t time to get to safety.