Driving

Driving Safely During Monsoon Season

What and When is the Monsoon?

The word “monsoon” has been around for hundreds of years.  It is derived from the Arabic word “mausim,” which means season.  In Dutch, it is monssoen, in Portuguese, it is moncao.  They all have the same meaning – a season of the year when the winds shift, bringing rainfall and wind storms.  The term “monsoon” first came to the English language when the British colonized India and experienced the trade winds blowing off the Indian Ocean and Bay of Bengal, bringing wind and heavy rain.

The term “monsoon” perfectly fits Arizona’s weather pattern.  Typically, our winds blow from the west and southwest, bringing dry air from Baja and the California deserts.  But every year, from June to September, the weather pattern shifts.  The winds blow from the south and southeast, bringing moisture from Mexico and the Gulf of California.

Until 2007, the start of the monsoon was announced when the average daily dew point reached 55 degrees or higher for 3 consecutive days.[1]  The whole dew point/relative humidity thing is a bit confusing.  Suffice it to say that the higher the dew point, the muggier it is and the more miserable we are. Our definition changed in 2008, when the National Weather Service decided to set firm dates for the monsoon.  As currently defined, the monsoon runs from June 15 through September 30.

Of course, the amount of monsoon rainfall varies from year to year.  National Weather Service records for Arizona go back to 1896.  According to those records, the wettest monsoon was 1984.  That year we got 9.56 inches of monsoon rain.  The driest year was 1924, when we received only 0.35 inches.

Monsoon Storms Can Bring Hazardous Driving Conditions.

Monsoon storms seldom last more than a few hours.  First, comes wind and dust, followed by thunder, lightning and heavy rain.  As quickly as it started, the storm is over.  The short duration of these storms gives many drivers the option of staying where they are and waiting for the storm to end.  Staying put is exactly what ADOT, the Arizona Department of Transportation, recommends.  Sometimes, we have no choice but to drive through a storm.  That’s especially true if you are already on the road when the storm hits.    If you must drive, be careful and watch out for hazardous conditions.  ADOT urges drivers to be prepared for the unexpected.  Keep an emergency kit in your car that includes water, blankets and flashlights with extra batteries.

Dust Storms: 

Dust storms or haboobs are an integral part of Arizona monsoon storms.  Veteran Arizona residents call them dust storms, but haboob is also correct.  “Haboob” is another Arabic word and means “blown.”  Haboobs are giant walls of dust created when collapsing thunderstorms generate high winds.  As the storm moves across the desert, cold air in front of the storm rushes down from the upper atmosphere.  The fast-moving, cold air stirs up sand and dust, blowing huge quantities up into the air.  As the storm moves, more and more dust is collected until a massive wall of dust blocks out the sun. That wall of dust may reach 1,500 – 3,000 feet in the air and be up to 100 miles wide.

The Phoenix area has experienced dust storms that are even bigger.  On July 5, 2011, a dust storm swept through the Phoenix Metropolitan area that was the biggest ever seen in the Valley of the Sun.  It was over 5,000 feet high and stretched the entire width of the Valley from Apache Junction to Goodyear.  That storm was pitch black with zero visibility.

One of the worst experiences is driving down the freeway and being hit by this massive wall of dust and sand.  Suddenly, your visibility goes from great to almost nothing.  You find yourself lost and blind.  If you are on the freeway and a dust storm hits, follow these precautions:

  • If possible, exit and wait out the storm;
  • If you are not near an exit, pull off the road as far to the right as possible;
  • Turn off your lights;
  • Set your parking brake and take your foot off the brake pedal;
  • Keep your seat belt buckled and wait for the storm to subside.

If you leave your headlights or brake lights on, you risk another driver following you off the road while thinking he is still in the travel lane.  If you are stopped somewhere when the haboob hits, stay in your car.  Dust storms contain metals and other particles that may be harmful.  You want to avoid breathing the dust into your lungs.  If you are forced to leave the car, keep your mouth and nose covered to protect your airway.

Flooded Roadways

Another major monsoon danger is flooded roadways.  City roadways often flood because trash and litter accumulate along roadways.  It doesn’t rain often enough in Arizona to keep the storm drains clear.  When rain hits, the trash and debris are washed into the storm drain, blocking the drains and the freeway pump stations.  On suburban and rural roadways, the nature of our soil contributes to flooding.  Monsoon rains are often intense.  In many areas of the state, just below the few inches of sandy soil is a layer of calcium carbonate or caliche.  The hard, clay-like caliche inhibits rain water from being absorbed into the ground.  Instead, the water runs from higher areas to low lying roads and underpasses.  In mountain areas, the runoff can cause flash floods- raging torrents rushing down gullies and washes, sweeping trees, branches and rocks along their path.

Over the years, we have had a number of flash flood deaths in Arizona.  Flash flooding can be deadly, and we must all be cautious.  Every year ADOT gives Arizona motorists the same advice, and every year some people ignore it.  DO NOT DRIVE INTO FLOODED AREAS, AND NEVER DRIVE AROUND BARRICADES.  The water does not need to be very deep.  A few inches of rapidly moving water can wrest control from your hands and shove your car along with the flood.  Moreover, you have no idea what is under the water.  The floodwaters may contain big rocks that could damage your car. 

Every year people drive into flooded areas and need to be rescued.  A few years ago, a medical transport driver, driving a wheelchair bound patient to an appointment, drove around a barricade into a flooded street in Scottsdale’s Indian Bend Wash.  The van became stuck in the swirling floodwater.  It took 30 firefighters from Scottsdale, Tempe, and Phoenix to engineer a rescue.   Because incidents like this happen all too often, Arizona has a Stupid Motorist Law, Arizona Revised Statutes, § 28-910.  The Stupid Motorist Law basically makes the driver responsible for the cost of rescue if he drives around a barricade or ignores a road closure sign and ends up needing rescue. 

The following are important tips to remember if you are caught driving during a monsoon rain storm.

  • Make sure your tires are in good condition. Bald or defective tires make driving in the rain even more hazardous.  Because rainfall is so infrequent, a thin layer of oil collects on roadways from passing cars.  When it starts to rain, the road becomes slick.
  • Replace your wiper blades. Wiper blades do not last long under our desert sun.  Inspect them frequently and replace them before they become too brittle to be effective.   When the rain is gushing down, working wiper blades are crucial.
  • Be aware of hydroplaning. Hydroplaning occurs when a thin layer of water gets between your tires and the road.  Your car loses contact with the road surface, and you find yourself drifting or sliding.  You have no traction.  It is very similar to skidding on ice.  If you feel your car hydroplaning, take your foot off the gas; do not brake.  If you find yourself drifting to the side, gently turn the wheel in the direction of the slide.  With your foot off the gas, the car will slow, and you will regain traction.
  • Avoid travel lanes with standing or flowing water. Also, be wary of high profile vehicles.  They are more susceptible to heavy winds.  A sudden gust could push them into your lane.
  • Drive slowly and leave plenty of distance between you and the driver ahead. If you are following a large truck, keep well back.  Large tires throw up spray that can obscure your visibility.
  • Drive with your headlights on. You need to make yourself as visible as possible.
  • If traffic lights are out, treat the intersection like a 4 way stop, but be cautious. Not all drivers are content to wait their turn.
  • If you can, wait out the storm in a safe location.

Downed Power Lines

Another danger of monsoon storms is downed power lines.  If you spot a downed power line across a roadway, assume it is live and dangerous.  Do not approach the power line.  Stop at least 100 feet away.  High voltage electricity can travel through the ground, so keeping your distance is important.

If a power line falls across your car, stay in the vehicle.  Avoid touching anything metal either inside or outside the car.  You will need to wait for professional help to arrive.  Not all live power lines create sparks like they do on TV.  You have no way to know if the line is live until the fire department announces it is safe.  Never attempt to rescue a driver under a downed power line on your own.  The risk is just too great.

Stay Up To Date On Weather Conditions

During the monsoon, it is particularly important to stay alert for weather changes.  Before planning a trip, check weather and highway conditions.  If you get a severe storm warning on your phone, stay where you are and be safe.  You can get up to date information on highway conditions at ADOT’s website www.az511.gov, or you can dial 511 from anywhere in Arizona.

Resources

www.arizonamonsoondefensivedriving.com/

www.azdot.gov/about/transportation-safety/Weather/monsoons

www.az511.gov

 

 

[1]  Warmer air can hold more moisture than cold air.  The relative humidity is the amount of moisture in the air based on the amount of moisture the air can hold at that temperature.  Dew point is the temperature to which the air would need to be cooled to reach maximum saturation. A relative humidity of 100% means the dew point is equal to the current temperature and the air is completely saturated.

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