Storms

Hazards of Thunderstorms

Hurricane Ivan, Florida 2004

Waterspout - weak tornado that forms over water. Most common in along the Golf Coast and Southeastern states. Occasionally move inland and become tornados.

Damage from a tornado.

Lightning Two Major Types –Cloud to cloud Within a cloud or between clouds Sheet lightening 80% of all lightening –Cloud to grounds Base of a cloud to the surface Steps in lightning formation 1.Charge separation 2.Stepped leader - shaft of negatively charged particles. 3.Return stroke - electric current works its way upward 4.Dart leader 5.Repeat of stroke and dart leader several time produces a flash

Other (less common) types of lightning Ball lightening St. Elmo’s Fire Sprites Blue Jets Thunder - increase in temperature due to lightning causes the air to expand explosively producing a loud sound. Sound travels km/sec Light travels - 300,000 km/sec Count the number of the seconds between stoke and thunder and divide by three to determine distance of storm in kilometers

Air Mass Thunderstorms –Most common –< 1 hour –Relatively small Severe Thunderstorms –Less common –12 hrs. to several days –Intense, large storms Thunderstorms

Mesoscale convective Systems –Mesosscale Convective Clusters –Squal lines Supercell –Any severe thunderstorms can spawn tornadoes! Tornado - rotating storm at the base of a cumulonimbus cloud Starts from a mesocyclone Mesocyclone - rotating region with a cumulonimbus cloud that may form a tornado Severe Thunderstorms

Fujita Scale (F scale) - used to measure a tornado. Tornado watch - possiblity of a tornado in an area Tornado Warning - Tornado has been sighted in an area. –Issued by the NWS

Hurricanes The deadliest natural disaster in the US was the 1900 Galveston Hurricane 6000 people dead Hurricane - tropical storm that develops over the Atlantic and eastern Pacific. August - September is hurricane season typhoons - western pacific cyclones - Indian Ocean and Australia Most powerful of all storms. Covers areas 1000 times greater than tornado.

Hurricanes Eye - relatively calm center of the storm Eyewall - adjacent to the eye and most intense portion of the storm. Highest winds Storm surge - rise in sea level associated with hurricanes. Development of a hurricane 1.Tropical disturbance - disorganized group of thunderstorms 2.Tropical depression - zone of Low pressure develops 3.Tropical Storm - winds speeds 60 to 120 km/hr. 4.Hurricane - winds greater than 120km/hr.

The Saffir-Simpson Hurricane Scale Categor y WindsEffects One74-95 mphNo real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Also, some coastal road flooding and minor pier damage Two mphSome roofing material, door, and window damage to buildings. Considerable damage to vegetation, mobile homes, and piers. Coastal and low-lying escape routes flood 2-4 hours before arrival of center. Small craft in unprotected anchorages break moorings. Three mphSome structural damage to small residences and utility buildings with a minor amount of curtainwall failures. Mobile homes are destroyed. Flooding near the coast destroys smaller structures with larger structures damaged by floating debris. Terrain continuously lower than 5 feet ASL may be flooded inland 8 miles or more. Four mphMore extensive curtainwall failures with some complete roof strucutre failure on small residences. Major erosion of beach. Major damage to lower floors of structures near the shore. Terrain continuously lower than 10 feet ASL may be flooded requiring massive evacuation of residential areas inland as far as 6 miles. Fivegreater than 155 mph Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Major damage to lower floors of all structures located less than 15 feet ASL and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5 to 10 miles of the shoreline may be required.

Detecting Hurricanes Satellites –Needed for observing development of tropical storms because they develop over the oceans Aircraft –Fly directly into storms to collect detailed data of the structure of storms Radar –Doppler radar allows measurement of storm intensity, movement and development Buoys –Provide direct measurements of surface conditions during the storm

Hurricane Warnings and Watches Hurricane Watch - hurricane is a possible threat generally within 36 hours Hurricane Warning - Issued when hurricane conditions are expected in an area in less than 36 hours.