Hurricanes are tropical cyclones that form in the western hemisphere and the Atlantic Ocean. Tropical cyclones are the most complex and powerful storm systems on Earth. They pack all the hazards of the planet's atmosphere: torrential rain, lightning, hail, high speed winds, and tornadoes. And they all begin with calm winds swirling over very calm, warm waters.
As seen in the image above, hurricanes in the Pacific ocean form in the waters off western coast of Mexico and often move northwest, further into the ocean. Hurricanes that do head to the U.S., often lose strength or dissipate before reaching the west coast due to cooler water and upper-level wind shears. Hurricanes in the Atlantic ocean however, often pose a much greater threat. This is greatly due to the dry, hot winds that are blown westward from the Saharan desert.
Steps to a hurricane formation:
Hurricanes form at different times depending upon where they occur.
|Region||Start of Season||End of Season|
On average, the diameter of hurricane-force winds is about 100 miles. Slower speed winds further out from the storm center increase the storm system's diameter on average 300 to 400 miles across. And the eye of the hurricane is 30 miles in diameter.
A hurricane is dangerous no matter its size or strength. A hurricane's high winds, storm surges, heavy rains and tornadoes all pose a threat to anything in the hurricane's path. While that path varies from hurricane to hurricane, it is often the coastal states with heavily populated areas that bear the brunt of the destruction. Hurricane force wind strength is rated according to the Saffir-Simpson Hurricane Wind Scale. This scale estimates potential property damage according to the hurricane's sustained wind speed.
|Storm Category||Wind Speed||Damage Potential|
|Category 1||Very dangerous. Well-constructed frame homes could have damage to roof, tree branch damage. Some power loss.|
|Category 2||Extremely dangerous. Homes sustain major roof and siding damage. Shallow rooted trees snapped or uprooted. Near-total power loss is expected.|
|Category 3||Devastating damage. Major damage to house roof decking. Many trees uprooted or snapped. Electricity and water will be unavailable for several days or weeks.|
|Category 4||Catastrophic damage. Many home severely damaged, most trees snapped or uprooted. Power outages extensive, lasting weeks to months.|
|Category 5||Catastrophic damage. Most homes destroyed. Most of the area will be uninhabitable for weeks or months.|
In addition to high winds, a hurricane causes high tides. A normal ocean tide is about two feet tall. But when storm winds push up against the ocean surface, pulling up sea water, this forms a storm surge that piles on top of the normal tide. If a hurricane's winds add 15 feet on top of the normal two feet ocean tide, this produces a 17 food storm tide, which can very easily sweep away buildings, trees, cars, and people.
Storm tide height also depends on whether the tide is high or low. The worst case is when a hurricane has generated a storm tide during a normal high tide. High tides carry storm surges higher and help send them further inland.
Hurricanes can travel up to 100 – 200 miles inland. However, once a hurricane moves inland, it can no longer draw on heat energy from the ocean and weakens rapidly to a tropical storm (39 to 73 mph winds) or tropical depression. As hurricanes move inland, they unleash torrential rains, thus the greatest damage inland comes from flooding. Inland towns in mountainous regions are especially vulnerable to flash flooding. Rain strikes mountain sides and rushes down to the rivers, quickly inundating towns as it goes. Rain from Tropical Storm Bill (2015) dumped 10 inches of rain to west Texas, causing surging floods throughout creek and river valleys. Flash flooding in Austin and San Antonio metro areas required multiple high water rescues. Hurricanes and their remnants have struck every state in the Union.
Since hurricanes develop in the ocean, it is easy to detect the coming of a hurricane before it hits inland. Weather forecasters will know several hours to several days before the arrival of a hurricane, providing ample time for preparation. Make sure to follow your local weather news channel for alerts.
2 days before landfall: Conditions remain the same. This is when a hurricane watch is issued.
26 hours before landfall: First signs of a hurricane appear including falling pressure, light breezes, ocean surface swells of 10-15 feet, and white cirrus clouds on the horizon.
24 hours before landfall: Overcast skies, high winds, sea foam on the ocean's surface. It is best to remain indoors and make storm preparations.
6 hours before landfall: There will be 90 + mph winds,the storm surge has advanced, and it will be nearly impossible to stand upright outside.
Decide if you are going to take shelter in place or evacuate.
Buis, Alan. "Could a Hurricane Ever Strike Southern California?" Jet Propulsion Laboratory - California Institute of Technology, NASA, 17 Oct. 2012, www.jpl.nasa.gov/news/news.php?release=2012-329.
"Saffir-Simpson Hurricane Wind Scale." National Hurricane Center, National Oceanic and Atmospheric Administration, www.nhc.noaa.gov/aboutsshws.php.
"Storm Surge Overview." National Hurricane Center, National Oceanic and Atmospheric Administration,www.nhc.noaa.gov/surge/.