This evenings spotter tips deal with estimating wind speeds.
The most prevalent severe weather in Hillsborough County during the Spring and Summer is damaging thunderstorm winds. These strong winds knock down trees...take off roofs...and cause other structural damage. Reports of these winds and the damage they cause are important to the National Weather Service in helping to define which storms are producing severe weather. The more accurate your wind speed estimates are...the more helpful they are to the forecasters,
High winds are not limited to the spring and summer months, however. Fall brings tropical cyclones, and winter brings nor'easters. High winds can be associated with both of these types of weather.
There are generally three wind scales used in common practice: the Fujita scale for measuring tornadoes, the Saffir/Simpson scale for measuring hurricane damage potential, and the Beaufort scale for measuring wind in general.
Lets start with the Fujita or F-Scale. It applies to the strength of tornadoes, and runs from F0 to F5.
F0 and F1, or minor tornadoes have wind speeds on the order of 110 mph. Winds of this speed will peel back roof shingles, and push moving automobiles off the road.
F2 and F3, or moderate tornadoes have wind speeds between 113 and 205 mph. Winds of this strength will tear off roofs and walls, snap large trees, and lift cars off the ground.
F4 and F5, or severe tornadoes have winds between 206 and 318 mph. A tornado of this type will level a well constructed house, blow structures a distance off of their foundations, and sweep the ground clear of debris.
The Saffir/Simpson scale is used to classify the damage potential of a tropical cyclone. Storms of this nature fall into categories ranked from 1 to 5.
A Category 1, or minimal hurricane, has winds between 74 and 95 mph.
A Category 2, or moderate hurricane, has winds between 96 and 110 mph.
A Category 3, or extensive hurricane, has winds between 111 and 130 mph.
A Category 4, or extreme hurricane, has winds between 131 and 155 mph.
A Category 5, or catastrophic hurricane, has winds greater than 155 mph.
The Beaufort scale of wind speeds was originally developed for estimating winds at sea, but has been adapted for use on land. The scale runs from Beaufort Force 0...calm, to Force 12...Hurricane or wind speeds greater than 74 mph.
Here is a simplified guide to estimating winds.
If large tree limbs are in motion and the wind whistles through wires...winds are between 25 and 30 mph.
When whole trees are in motion and it is difficult to walk against the wind...winds are between 30 and 40 mph.
When twigs break off trees or the wind generally impedes you from walking...and slight structural damage is done to chimneys or shingles...estimate winds between 40 and 55 mph. Start reporting to NWS if winds reach this level!
If the winds are causing widespread damage to roofs and antennas; and shallow rooted trees are pushed over...the winds are between 55 and 70 mph.
If roofs begin to peel off; windows are broken; small trailers are moved or overturned; or moving vehicles are pushed off the road...estimate the winds over 70 mph.
Winds of this speed can occur from downburst or straightline winds in any thunderstorm, tornadoes, and hurricanes.
In coming weeks we will look more closely at each of these types of weather.
This script as well as more information on this topic can be found at the following web site: http://www.qsl.net/kb1dfe.