But They Don’t Come Here, Or Do They?

Satellite View Of A Hurricane | Image by picasaweb.google. com

I’m talking about hurricanes. The Atlantic-Caribbean Tropical storm/hurricane season officially  begins on Sunday June 1st and continues through November 30th. The Western Pacific Tropical storm/hurricane season has already begun with hurricane Amanda. Why should we be concerned about hurricanes? They don’t bother the Pacific Northwest, or do they? The answer is not as simple as you might think. First, we need to look at where hurricanes form. Many disturbances develop over Western Africa and move westward over the Atlantic Ocean.

Structure of a tropical cyclone, High pressure above returns airflow down | Image by compare Infobase Limited
Structure of a tropical cyclone, High pressure above returns airflow down | Image by www.mapsoftheworld.com

They start out as tropical waves and once they move over the ocean they can continue to grow as long as the water temperature is 85 degrees F. or warmer. Also, there must be high pressure aloft to keep a cap over the tropical cyclone to force air back down into it. Without the high pressure above the warm moist air would keep rising and eventually the storm would fall apart because it would run out of that tropical moisture.They then can move through the islands and swing more to the north into the Gulf of Mexico or along the US east coast. Occasionally one will cross Central America and end up in the Pacific Ocean where, if it has gained tropical storm status, it will be given a new name.

There is a basic pattern to the major ocean currents that effect the North American Continent. A map of the world shows how first the tropical depression (sustained winds up to 38 mph), then the tropical storm (sustained winds 39-73 mph), and finally the hurricane (sustained winds 74 mph or higher),if it gets strong enough, follow the path of the sea surface currents.  In the Atlantic they move from the African continent through the Caribbean Sea and along the eastern seaboard of the United States. In the Pacific the sea surface currents push down from the north and flow to the south parallel to the Pacific coastline. That makes it nearly impossible for a hurricane to move from off the coast of Mexico northward to the Pacific Northwest. There are times when we will get clouds and moisture moving up from a disturbance off the Mexican coast, but the disturbances turn to the west or northwest away from us.

The upper air wind patterns also help to determine the path these tropical disturbances can take. The “Bermuda High” sits over the North Atlantic Ocean and with its clockwise rotation spins the airflow around to the east and then swings it to the southwest over Northeast South America, northwest into the Gulf of Mexico, then northeastward toward the US East Coast hugging the coast and continuing along the Southeast Coast of Canada.

Pacific High air circulation (shows sea level pressures) | Image by USAToday.com
Pacific High air circulation (shows sea level pressures) | Image by USAToday.com

Another High Pressure Center sits over the North Pacific Ocean and is called the “Pacific High.” Its clockwise circulation moves the airflow from the Northwest to the South and Southeast parallel to the West Coast of the US. If you take a look at these two Summer-time High Pressure centers you will see that the airflow would send hurricanes on the Atlantic side into the Gulf of Mexico and up the East Coast predominately.

The Jet Stream has two branches that can cross the US. The Polar Jet Stream to the North brings down colder air from the North and pushes it across the US and the Subtropical Jet Stream to the South which brings in warmer moist air and pushes it across the US. They help steer the surface storms across the North American continent. Their positions determine whether we have surface storms moving through the Pacific Northwest. The Jet Stream also can steer tropical storms and hurricanes if they are under the swift moving river of air.

As we’ve seen there are many forces that deflect tropical storms and hurricanes away from the Pacific Northwest. Since that has been shown why should we want to keep up with tropical disturbances. One good reason is that many of us have relatives and friends who do live where hurricanes can strike and we are interested in seeing that they will survive the potential hit from one of these destructive killing machines. Another reason is that though the odds are against it happening, a hurricane could potentially find a way to sneak up on us.

Damage in Corvallis due to Columbus Day storm | OSU Archives
Damage in Corvallis due to Columbus Day storm |
OSU Archives

A good example is “the Columbus Day storm.” There was a remnant of a former Typhoon (Western and Central Pacific hurricane) that did hit Oregon with devastating effects and that was the Columbus Day storm of 1962. It was a dead Typhoon that came all the way across the Pacific Ocean and combined with a Gulf of Alaska storm and smashed through the Pacific Northwest. As many as 46 deaths and hundreds of injuries were attributed to the storm which produced wind gusts measured to 145 mph. It was the second deadliest storm in Oregon history according to Kathie Dello, director of the Oregon Climate Service at Oregon State University.

When a disturbance gets strong enough to be called a tropical storm it is given a name. Since 1953 Atlantic tropical storms had been named from lists originated by the National Hurricane Center. That job is now performed by an international committee of the World Meteorological Organization. Here are the tropical storm names for the 2014 Atlantic/Caribbean tropical storm season: Arthur, Bertha, Cristobal, Dolly, Edouard, Fay, Gonzalo, Hanna, Isaias, Josephine, Kyle, Laura, Marco, Nana, Omar, Paulette, Rene, Sally, Teddy, Vicky, and Wilfred. A name is discarded when the storm turns out to be a killer and/or very destructive to property.

If you want to follow the tropical storms more closely there is a website that it just what you need. It is the National Weather Service National Hurricane Center Home Page. They also have grid charts you can print out so you can plot their movements yourself.

Let me know what you would like me to talk about or explain. You can comment below or email me at: [email protected].

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