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Hurricanes


Hurricane Charley 2004

 

In recent years, hurricanes have almost become synonymous with Florida in the thoughts of many across the country. Close to the tropics and surrounded on three sides by warm water, Florida can be particularly vulnerable to these systems as they develop and move generally westward across the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea. During a typical year, one or more tropical storms or hurricanes threaten to impact portions of the state.

The Atlantic hurricane season officially begins on June 1st and continues through November 30th. Although the number of tropical storms and hurricanes typically peaks during August and September, it is important to remember that Florida can be impacted by tropical weather systems any time during the six-month-long season.

When a cyclonic (counter-clockwise flow) circulation develops at sea level, coincident with persistent thunderstorm activity, the weather system is designated a Tropical Depression. Once sustained winds in the weather system reach 39 mph, the system is classified as a Tropical Storm. If winds increase further and reach 74 mph or greater, the system is declared a Hurricane. Hurricanes with winds 111 mph or greater are designated Major Hurricanes, and are capable of catastrophic damage.



Hurricane Hazards

Hurricanes and tropical storms bring storm surge and coastal flooding, flooding from heavy rain, and tornadoes. For those away from the immediate coastline, inland flooding and tornadoes are often the most hazardous impacts from these systems.


Tornadoes associated with tropical systems typically form in the right-front quadrant of the circulation, relative to the direction of forward motion. If viewing the tropical system as a clock, this would be the area from noon to three o’clock in the direction that the storm is traveling. While normally not as intense as tornadoes produced by non-tropical severe thunderstorms, these tornadoes often move at speeds of 50 mph or greater. Regardless of origin, all tornadoes have the potential to be damaging and deadly. Another common area for tornado development is within the far outer rain bands, often hundreds of miles away from the tropical cyclone center. These tornadoes can affect locations that otherwise would not experience direct impacts from the tropical storm or hurricane.


Flooding from tropical cyclones is not correlated with the intensity of the system, but instead is related to the speed of forward motion. Slow moving tropical storms and hurricanes often produce large amounts of rain, which can lead to significant inland flooding. As with tornadoes, flooding impacts can occur hundreds of miles away from the cyclone center, or from the remnants of a former tropical system.


Flooding from torrential rains can produce a lot of damage. In fact, Florida’s record for the most rainfall in a 24-hour period came from a hurricane. Hurricane Easy in 1950 dumped more than three feet of rain in Yankeetown along the northern Gulf Coast in Levy County.


Other recent storms, such as Hurricane Irene in 1999, Hurricanes Frances and Jeanne in 2004 and Hurricane Katrina in 2005, caused extensive flooding of many streets and neighborhoods across Florida. In some cases, streets and towns were flooded for days after the storm.

 

Flood

Storm surge is the term used to describe the wall of water that is pushed toward the shoreline as a hurricane moves onshore. Storm surge combines with the local tide and the battering, wind-driven waves to push a tremendous volume of water onto the shore, often resulting in significant damage. In the strongest hurricanes, this storm surge can be as high as 15 to 20 feet above normal water levels. The combination of rising water and pounding waves is often deadly. Worldwide, approximately 90 percent of all deaths in hurricanes are caused by drowning in either storm surge or rainfall flooding. Those living in coastal and near-coastal communities should know if or in which evacuation zone they reside, as well as the elevation of their property. When local officials declare an evacuation for your area, move to the nearest evacuation destination outside of the danger zone. Your may choose to stay with friends or relatives, at a hotel/motel, or at an evacuation shelter.


Damage from Hurricane Ivan in 2004.

Winds are the most well-known impact of tropical storms and hurricanes. The highest winds occur just outside the eye (or center), within a region referred to as the eye-wall. Hurricane force winds can easily damage or destroy mobile homes and other non-permanent structures, often moving them well away from their foundations. Roofs, pool enclosures, trees, and power lines are also frequently damaged by hurricane force winds. Although the winds of a hurricane typically weaken rapidly following landfall, Florida’s flat terrain and narrow width allow strong winds to survive farther inland than other parts of the country. In August 2004, Hurricane Charley made landfall in southwest Florida, exhibiting a fast forward motion of 25 mph (nearly twice the typical speed for Florida hurricanes) and brought hurricane force winds to the Orlando Metro area – over 100 miles inland from the point of landfall.

The strongest hurricanes can have winds in excess of 155 miles per hour. Storms of such strength are classified as Category 5 hurricanes on the Saffir-Simpson hurricane scale. Hurricane Andrew, which struck South Florida in 1992, was the last Category 5 hurricane to make landfall in the United States, causing almost $30-billion in damage and killing a total of 40 people.

Detecting and forecasting hurricanes

The National Hurricane Center in Miami tracks tropical systems from their birth until they make landfall and dissipate, or move out over cold waters. Meteorologists use several data sources to observe and track developing tropical storms and hurricanes. When systems are developing very far from land, satellite imagery is used to locate the center and estimate the strength of the winds.

Recon planes imageOnce meteorologists know a storm’s location and strength, the next step is to predict its track and strength out to five days. To do this, meteorologists use very sophisticated aids known as computer models, which take in numerous amounts of data and produce their own forecasts. One of the most important jobs of the hurricane forecaster is to determine which model is the best for a particular forecast. The official forecast is then issued by the National Hurricane Center, and National Weather Service offices all across Florida step in to provide locally specific information on the storm’s potential effects in your neighborhood.


Planning for a Hurricane

Planning in advance for possible impacts will go a long way toward keeping your family safe when a tropical storm or hurricane affects your area. Be prepared before the hurricane season begins by having a family disaster plan, as well as an emergency supply kit. Review and update your family disaster plan prior to each season. When a storm threatens, the National Hurricane Center, together with your local National Weather Service forecast office, will issue Tropical Storm and Hurricane Watches and Warnings in plenty of time for you to prepare for a storm. Watches are issued 48 hours in advance of the time damaging winds are possible within the specified area. Warnings are issued 36 hours prior to the time when damaging winds are expected. Remain informed of possible threats throughout the season, and put your plan into action when the time comes. Following this advice will help keep you and your family weather-safe.


Hurricane Preparedness Week is May 28 - June 1, 2012

 

Saffir-Simpson Scale

Tropical Storm Winds 39 73 mph Flooding becomes a great danger.
Category 1 Hurricane Winds 74-95 mph. No real damage to buildings. Damage to unanchored mobile homes.
Category 2 Hurricane Winds 96-110 mph. Some damage to building roofs, doors and windows. Considerable damage to mobile homes. Some trees blown down.
Category 3 Hurricane  111-130 mph. Some structural damage to small homes. Large trees blown down. Mobile homes and poorly built signs destroyed.
Category 4 Hurricane Winds 131-155 mph. Wall failures in homes and complete roof structure failure on small homes. Total destruction of mobile homes. Trees, shrubs and signs all blown down.
Category 5 Hurricane Winds Greater than 156 mph. Complete roof failure on homes and industrial buildings. Some complete building failures.



What's it like to go through a hurricane on the ground? What are the early warning signs of an approaching tropical cyclone?

Just as every person is an individual, every hurricane is different so every experience with a storm will be unique. The summary below is of a general sequence of events one might expect from a Category 2 hurricane approaching a coastal area. What you might experience could be vastly different.

  • 96 hours before landfall
    At first there aren't any apparent signs of a storm. The pressure is steady, winds are light and fair weather clouds dot the sky. The perceptive observer will note a swell on the ocean surface of about three feet in height with a wave coming ashore every ten seconds. These waves race out far ahead of a storm at sea, but could easily be masked by locally wind-driven waves.

  • 72 hours before landfall
    Little has changed, except that the swell has increased to about six feet in height and the waves now come in every nine seconds. This means that the storm, still far over the horizon, is approaching.

  • 48 hours before landfall
    If anything, conditions have improved. The sky is now clear of clouds, the pressure is steady, and the wind is almost calm. The swell is now about nine feet and coming in every eight seconds. A hurricane watch is issued, and areas with long evacuation times are given the order to begin evacuating.

  • 36 hours before landfall
    The first signs of the storm appear. The pressure is falling steadily, the winds pick up to about 10-20mph, and the ocean swell is about 10-12 feet in height and coming in every five to seven seconds. On the horizon a large mass of white cirrus clouds appear. As the veil of clouds approaches it covers more of the horizon. A hurricane warning is issued and low lying areas and people living in mobile homes are ordered to evacuate.

  • 24 hours before landfall
    In addition to the overcast, low clouds streak by overhead. The pressure continues to fall and the wind picks up to 35 mph. The wind-driven waves are covered in whitecaps and streaks of foam begin to ride over the surface. Evacuations should be completed and final preparations made by this time.

  • 18 hours before landfall
    The low clouds are thicker and bring driving rain squalls with gusty winds. Winds are whistling by at 40 mph. It is hard to stand against the wind.

  • 12 hours before landfall
    The rain squalls are more frequent and the winds don't diminish after they depart. The pressure is falling rather rapidly. The wind is howling at hurricane force at 74 mph, and small, loose objects are flying through the air and branches are stripped from some trees. The sea advances with every storm wave that crashes ashore and the surface is covered with white streaks and foam patches.

  • Six hours before landfall
    The rain is constant now and the wind, now around 90 mph, drives it horizontally. The storm surge has advanced above the high tide mark. It is impossible to stand upright outside without bracing yourself, and heavy objects like coconuts and plywood sheets become airborne missiles. The wave tops are cut off and make the sea surface a whitish mass of spray.

  • One hour before landfall
    It didn't seem possible, but the rain has become heavier, a torrential downpour. Low areas inland become flooded from the rain. The winds are roaring at 105 mph, and the pressure is falling rapidly. The sea is white with foam and streaks. The storm surge has covered coastal roads and 16 foot waves crash into buildings near the shore.

  • The eye
    Just as the storm reaches its peak, the winds begin to slacken, and the sky starts to brighten. The rain ends abruptly and the clouds break and blue sky is seen. However, the pressure reaches its lowest point and the storm surge reaches the furthest inland. Wild waves crash into anything in the grasp of the surge. Soon the winds fall to near calm, but the air is uncomfortably warm and humid. Looking up you can see huge walls of cloud on every side, brilliant white in the sunlight. The winds begin to pick up slightly and the clouds on the far side of the eyewall loom overhead.

  • One hour after landfall
    The sky darkens and the winds and rain return just as heavy as they were before the eye. The storm surge begins a slow retreat, but the monstrous waves continue to crash ashore. The pressure is now rising, the winds top out at 105 mph, and heavy items torn loose by the front side of the storm are thrown about and into sides of buildings that had been facing away from the storm’s winds before the eye passed.

  • Six hours after landfall
    The flooding rains continue, but the winds have diminished to 90 mph. The storm surge is retreating and pulling debris out to sea or stranding seaborne objects well inland. It is still impossible to go outside.

  • 12 hours after landfall
    The rain now comes in squalls and the winds begin to diminish after each squall passes. The wind is still howling at near hurricane force at 70 mph, and the ocean is covered with streaks and foam patches. The sea level returns to the high tide mark.

  • 36 hours after landfall
    The overcast has broken and the large mass of white cirrus clouds disappears over the horizon. The sky is clear and the sun seems brilliant. The winds are a steady 10 mph. All around are torn trees and battered buildings. The air may smell of vegetation and muck that was pulled up by the storm from the bottom of the sea to cover the shore. Local officials begin response efforts and some municipalities may give notice for residents to return.

diagram of the timeline of a hurricane

Hurricane Tracking Maps

Here are some tracking maps available to help monitor the direction of tropical storms or hurricanes.



Rainfall Rule of Thumb

To estimate the total rainfall in inches from a hurricane, divide 100 by the forward speed of the storm in miles per hour 100 / forward speed = estimated inches of rain.
Your local Weather Forecast Office may have a more accurate estimation method for your area.

  • Know if you live in an evacuation area. Know your home’s vulnerability to storm surge, flooding and wind. Have a family plan.
  • At the beginning of hurricane season (June), check your supplies, replace batteries and rotate your stock of food and water.
  • If a storm threatens, listen to your local authorities. Evacuate if ordered.

Updated:

January 11, 2012 16:18