Protecting your Peace of Mind

Protecting your Peace of Mind

If you are moving into an area that can be affected by tropical storms, try to avoid living in a place where you may be at risk of storm surge. Also, creeks and rivers, while picturesque, could become disasters areas during a flood; stick to higher ground. Anything to can do to minimize the future impact of a tropical cyclone on your home will be one less thing to worry about if the event occurs.

Remember, past experiences of tropical cyclones are NO measure of future events. There may, and probably will be times, when you return to your home, after evacuating, to find no damage whatsoever as the storm either weakened or turned away from where we thought it would strike. However, the time you spent preparing your home and loved ones was NOT wasted because the next time you may not be so fortunate.

You may hear some of the "locals" make statements like "I've lived here x-number of years made it through storms such-and-such" or "a certain hill or creek protected us at this-or-that place". While you cannot discount their experiences, you can know they were fortunate during those events. It's best to be prepared. This could be the year a tropical cyclone could bring devastating results.

For your peace of mind, always heed your local official’s instructions. It is their responsibility to serve your community. If you follow their guiding, you will make their job much easier. If they ask you to evacuate, do so immediately. This way, you will not be a burden on the local rescue teams so they can better assist the ones who may need rescue through no fault of their own.

Your evacuation will also aid the police after the storm passes. Unfortunately, some people try to take advantage of others going through difficult situations. While generally not widespread, looting does occur in neighborhoods damaged by tropical storms. Your absence will help the police better monitor the region and make it easier to spot the ones who do not belong.

One final word of caution. You may live thousands of miles from the effects of tropical cyclone and think you can not be a victim. However, that is not always the case. Vehicles that have been flooded are supposed to be relegated for salvage but many are not. The unscrupulous do superficial cleaning jobs on the vehicles and wholesale them to dealers across the nation. If you are considering purchasing a used vehicle, be sure to check the title history and hire a trusted mechanic to do a thorough inspection including checking behind the door panel for signs of flooding. A few dollars spent now could save your thousands of dollars down the road and maybe a life.

El Niño Southern Oscillation (ENSO)

From December 1997, this image shows the change of sea surface temperature from normal. The bright red colors (water temperatures warmer than normal) in the Eastern Pacific indicate the presence of El Niño.

One of the most prominent aspects of our weather and climate is its variability. This variability ranges from small-scale phenomena such as wind gusts, localized thunderstorms and tornadoes, to larger-scale features such as fronts and storms to multi-seasonal, multi-year, multi-decade and even multi-century time scales.

Typically, long time-scale events are often associated with changes in atmospheric circulations that encompass vast areas. At times, these persistent circulations occur simultaneously over seemingly unrelated, parts of the hemisphere, and result in abnormal weather, temperature and rainfall patterns worldwide.

El Niño is one of these naturally occurring phenomenons. The term El Niño (the Christ child) comes from the name Paita sailors called a periodic ocean current because it was observed to appear usually immediately after Christmas. It marked a time with poor fishing conditions as the nutrient rich water off the northwest coast of South America remained very deep. However, over land, these oceans current were heavy rains in very dry regions which produced luxurious vegetation.

Further research found that El Niño is actually part of a much larger global variation in the atmosphere called ENSO (El Niño/Southern Oscillation). The Southern Oscillation refers to changes in sea level air pressure patterns in the Southern Pacific Ocean between Tahiti and Darwin, Australia.

During El Niño conditions, the average air pressure is higher in Darwin than in Tahiti. Therefore, the change in air pressures in the South Pacific and water temperature in the East Pacific ocean, 8000 miles away, are related.

With the occurrence of warmer than normal temperature in the Eastern Pacific it stands to reason that there will be periods where the water temperature will be cooler than normal. The cooler periods are called La Niña. By convention, when you hear the name El Niño it refers to the warm episode of ENSO while the cool episode of ENSO is called La Niña.

ENSO is primarily monitored by the Southern Oscillation Index (SOI), based on pressure differences between Tahiti and Darwin, Australia. The SOI is a mathematical way of smoothing the daily fluctuations in air pressure between Tahiti and Darwin and standardizing the information. The added bonus in using the SOI is weather records are more than 100 years long which gives us over a century of ENSO history.

Sea surface temperatures are monitored in four regions along the equator:

• 
  Niño 1 (80°-90°W and 5°-10°S)
  
• 
  Niño 2 (80°-90°W and 0°-5°S)
  
• 
  Niño 3 (90°-150°W and 5°N-5°S)
  
• 
  Niño 4 (150°-160°E and 5°N-5°S)
  

Conversely, when the pressure in Tahiti is higher than Darwin, Australia the temperature in Niño 3.4 is lower than normal and La Niña is occurring; the cool episode of ENSO.

What is surprising is these changes in sea surface temperatures are not large, plus or minus 6°F (3°C) and generally much less. However these minor changes can have large effects our global weather patterns.

Effects of ENSO in the Pacific

Normal Conditions

Normally, sea surface temperature is about 14°F higher in the Western Pacific than the waters off South America.

This is due to the trade winds blowing from east to west along the equator allowing the upwelling of cold, nutrient rich water from deeper levels off the northwest coast of South America.

Also, these same trade winds push water west which piles higher in the Western Pacific. The average sea-level height is about 1½ feet higher at Indonesia than at Peru.

The trade winds, in piling up water in the Western Pacific, make a deep 450 feet (150 meter) warm layer in the west that pushes the thermocline down there, while it rises in the east.

The shallow 90 feet (30 meter) eastern thermocline allows the wind to pull up water from below, water that is generally much richer in nutrients than the surface layer.

El Niño Conditions

However, when the air pressure patterns in the South Pacific reverse direction (the air pressure at Darwin, Australia is higher than at Tahiti), the trade winds decrease in strength (and can reverse direction).

The result is the normal flow of water away from South America decreases and ocean water piles up off South America. This pushes the thermocline deeper and a decrease in the upwelling.

With a deeper thermocline and decreased westward transport of water, the sea surface temperature increases to greater than normal in the Eastern Pacific. This is the warm phase of ENSO, called El Niño.

The net result is a shift of the prevailing rain pattern from the normal Western Pacific to the Central Pacific. The effect is the rainfall is more common in the Central Pacific while the Western Pacific becomes relatively dry.

La Niña Conditions

There are occasions when the trade winds that blow west across the tropical Pacific are stronger than normal leading to increased upwelling off South America and hence the lower than normal sea surface temperatures.

The prevailing rain pattern also shifts farther west than normal. These winds pile up warm surface water in the West Pacific. This is the cool phase of ENSO called La Niña.

What is surprising is these changes in sea surface temperatures are not large, plus or minus 6°F (3°C) and generally much less.

Weather Impacts of ENSO

The Jetstream

As the position of the warm water along the equator shifts back and forth across the Pacific Ocean, the position where the greatest evaporation of water into the atmosphere also shifts with it. This has a profound effect on the average position of the jet stream which, in turn, affects the storm track.

During El Niño (warm phase of ENSO), the jet stream's position shows a dip in the Eastern Pacific. The stronger the El Niño, the farther east in the Eastern Pacific the dip in the jetstream occurs. Conversely, during La Niña's, this dip in the jet stream shifts west of its normal position toward the Central Pacific.

The position of this dip in the jet stream, called a trough, can have a huge effect on the type of weather experienced in North America.

During the warm episode of ENSO (El Niño) the eastern shift in the trough typically sends the storm track, with huge amounts of tropical moisture, into California, south of its normal position of the Pacific Northwest.

Very strong El Niños will cause the trough to shift further south with the average storm track position moving into Southern California.

During these times, rainfall in California can be significantly above normal, leading to numerous occurrences of flash flood and debris flows. With the storm track shifted south, the Pacific Northwest becomes drier and drier as the tropical moisture is shunted south of the region.

The maps (right) show the regions where the greatest impacts due to the shift in the jet stream as a result of ENSO. The highlighted areas indicate significant changes from normal weather occur. The the magnitude of the change from normal is dependent upon the strength of the El Niño or La Niña.

Tropical Cyclones

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  A substantial reduction in cyclone numbers,
  
• 
  A 60% reduction in numbers of hurricane days, and
  
• 
  An overall reduction in system intensity.