Thunderstorms, Hurricanes and Tornadoes
Thunderstorm Facts
• Right now there are about 2,000 thunderstorms occurring worldwide
• There are about 45,000 thunderstorms per day!!
• U.S. gets 100,000 per year!
Severe Thunderstorms
• Torrential Downpours
• Strong winds at greater than 58 mph
• Hail ¾ inch diameter (or larger)
• Frequent lightning
Severe Thunderstorm Watch
• Issued by National Weather Service
• This means that conditions are favorable for a thunderstorm
• Length is multiple hours.
Severe Thunderstorm Warning
• Issued By Local Weather Service
• Means a severe storm has been spotted by doppler radar
• Usually only an hour
Lightning
Types of Lightning
• Cloud-to-ground (CG)
• Intra-cloud (IC)
• Ribbon lightning
• Sheet lightning
• Heat lightning
• Ball lightning
Cloud-to-ground (CG) Lightning
Intra-cloud (IC) Lightning
Ribbon Lightning
Sheet Lightning
Heat Lightning
Ball Lightning
Lightning Safety
• Stay indoors, away from doors and windows.
• Do not take baths or showers.
• Do not use phones with cords.
• Cars are pretty safe…
Thunder
How Far Away Was That Lightning?
• When you see the flash, start counting seconds.
• When you hear the thunder, stop counting.
• Every 5 seconds is equal to 1 mile.
Tornadoes
F-Scale
• F0 – Light damage
• F1 – Moderate damage
• F2 – Considerable damage
• F3 – Severe damage
• F4 – Devastating damage
• F5 – Incredible damage (Auntie Em!)
Tornado Watch
• Conditions are favorable for a tornado to form
Tornado Warning
• A tornado has formed.
Tornado Safety
• Get indoors and stay there
• Stay away from doors and windows
• Get to lowest level possible
• Don’t get near things that can fall on you
When to expect
• Hurricane season is June through November
• Peak is in September
Formation of Hurricanes
• Tropical Depression
• Tropical Storm
• Hurricane
Tropical Depression
• Cluster of organized thunderstorms
• Not very compact
• Sustained winds of at least 30 mph
• Given a number
Tropical Storm
• Winds above 39 mph
• Given a name
• More organized
• If hits land, most damage caused is by rainfall.
Hurricane
• Winds over 74 mph
• Well defined center of circulation
• Eye Wall
• Damage from includes:– Wind– Storm surge– Rain
Pressure in hurricane
• A way to tell strength of hurricane is by its pressure
• Measured in millibars (mb)
• Higher pressures are weak, lower are stronger
Naming System
• A list of names from A-W (excluding Q)
• Alternate from male to female
• 6 lists, repeated in cycle
• Big name storms replaced
Saffir-Simpson Scale
• Designed by Herbert Saffir and Bob Simpson
• Divides hurricanes into categories based on maximum sustained winds.
Category 1
• Winds- 74-95 mph
• Storm Surge- 4-5 ft.
• Pressure- 986mb
• Damage- mobile homes, trees, minor costal flooding
Category 2
• Winds- 96-110 mph
• Storm surge- 6-8 ft.
• Pressure- 965- 979 mb
• Damage- Some roof and window. Damage to piers on coast. Small crafts. vegetation
Category 3
• Winds- 111-130 mph
• Storm surge- 9-12 ft.
• Pressure- 945-964 mb
• Damage- structure damage to homes and buildings. Mobile homes destroying. Major coastal flooding with a potential for inland flooding.
Category 4
• Winds 131-155 mph
• Storm surge- 13-18 ft.
• Pressure- 920-944 mb
• Damage- Complete roof damage. Major erosion to beaches. Further inland flooding.
Category 5
• Winds- Greater than 156 mph
• Storm surge- over 19 ft.
• Pressure- less than 920 mb
• Damage- Roofs torn off, buildings collapse, major inland flooding.
Hurricane Watch
• A hurricane poses a possible threat within the next 36 hours
Hurricane Warning
• Hurricane conditions expected within 24 hours
Most Damaging Storms
• 1) Katrina (2005)- 75 billion
• 2)Andrew (1992) 34 billion
• 3)Charley (2004)- 14 billion
• 4) Ivan (2004)- 13 billion
• 5) Wilma (2005)- 12 billion
• ..9) Agnes 1972 8.6 billion
Hurricane Safety
• Best plan is to evacuate– Towns have voluntary evacuation during a
watch, and some switch to mandatory during a warning.
• Plan early in advance
IF you choose to stay
• Board all windows
• Prepare Flashlights, avoid candles
• Stay tuned to radio
• Stay indoors