Summer Weather Awareness
[ UV Index ] - [ Heat & Humidity ] - [ Hurricanes ]
UV Index

A daily threat for much of the year, ultraviolet (known commonly as UV) rays are especially present in summer. The scale goes from 0-14 and is divided into categories from Low to Extreme.



In St. John's, the highest UV observations are usually '8' or 'Very High' however higher readings can happen under ideal conditions. Concrete, asphalt, sand, water, snow and ice are common surfaces that help reflect and thus increase UV rays and can further damage the skin. Snow is very reflective as it can reflect 50%-80% of UV rays. Altitude also affects the UV index. As air thickness decreases with higher altitide, the higher in altitude one is, the higher the UV Index.
Once levels of '11' or 'Extreme' have been reached, skin is very susceptible to UV radiation and can burn in a matter of minutes. This category is very rare in Canada, even in southern Ontario.
This scale may look different from the old scale which is still used in the United States. In 2003 the World Meteorological Organization adopted the newly developed Canadian scale. The old way categorized ‘Low’ as 0-4 and did not have a 'Very High' category. A reading of '4' which is now considered 'Moderate' was once considered 'Low' and can easily burn skin if it is not protected from the sun.

Category
UV Index
Time to Burn (mins.)
Tips
LOW
0-2
45-60+
Little or no protection is required. Sunglasses and wide brimmed hats are a good idea to keep eyes and scalp protected.
MOD.
3-6
30-45
Try to protect any exposed skin and spend as much time outdoors in the shade as possible. Skin block with an SPF of at least 15 is required and must be reapplied after excessive sweating or swimming.
HIGH
6-7
20-30
Avoid exposing skin to sunlight during peak UV hours from 10am-4pm and reapply sun block of SPF 30 or more frequently.
VERY HIGH
8-10
20-
Skin can burn very easily and any time spent in direct sunlight should be avoided and/or minimized. Try to use sun block with an SPF of 45 where possible and reapply it often. Don't forget your back, neck, toes, and lips (many lip balm's have SPF's).
The times to burn indicated are general and may vary depending on skin type. For example, some dark skinned individuals may take hours to damage their skin even under 'Extreme' UV levels whereas someone with very pale skin which does not tan could burn in a matter of minutes. Also, many people think that a good base tan will protect them from the sun and that they do not need to apply sunscreen or cover up from the sun. This is very misleading, as a dark tan will only protect you as much as a sunblock with an SPF of only 2 to 4 would. People who work or spend a lot of time outside always need protection, no matter how dark their tan or natural skin colour.

This graph demonstrates the UV intensity observed in St. John's on an early summer's day and under a cloudless sky. From the first day of summer until mid-July, UV rays are at their peak between 13:00 NDT and 13:10 NDT. Even on cloudy, overcast days UV observations can still reach "high" levels.

Heat & Humidity

When a warm spell combines with elevated levels of humidity, the temperature on the thermometer may not reflect the temperature the human body feels. Our bodies naturally cool ourselves by sweating which helps us cool down as the sweat evaporates off the skin’s surface. When it is very humid, it makes it much more difficult for the sweat to evaporate. In fact when the relative humidity is above 90%, the sweat process stops altogether.
The humidex was invented to express in units Celsius how hot we really feel during muggy weather. To accompany the humidex, a range was invented to express the degree of discomfort felt by most people.

Humidex Range
Effects
20-29
Little or no discomfort.
30-39
Some discomfort.
40-45
Great discomfort. Avoid excertion and seek air conditionned places and make sure to keep well hydrated. Avoid coffee and alcohol. When the humidex hits or is forcast to excede 40 or higher, Environment Canada issues a Humidex Warning.
45+
Any humidex above 45 is dangerous. Take any measures possible to stay cool and check for signs of heat exhaustion or heat stroke such as dizziness, light headedness, and feeling hot but not sweating are good signs you should seek medical attention.
54+
Humidex values of 54 or greater (129°F) can cause imminent heat stroke. Keep yourself in cool places and pay close attention to children, the elderly, and those with heart conditions.


The humidex is not the same as the American 'Heat Index' and they are both calculated using different formulas. In Newfoundland, Humidex Warnings are very rare, maybe one or two every summer. The most common areas that are prone to Humidex Warnings are southern Manitoba, all of Ontario, southern and eastern Québec, and the Maritimes.
Hurricanes

Known around the world also as ‘cyclones’ and ‘typhoons’, hurricanes are one of natures’ most violent storms. Normally once hurricanes reach Atlantic Canada they have lost strength and been downgraded to tropical storms or tropical depressions. The effects of the remnants of these storms are usually no more than strong winds and heavy rain, however this is not always the case and I have the proof! Looking back to records from September 19th, 2001, 155.2mm of rain fell, most of which in less than 6 hours when Hurricane Gabrielle passed just east of the Avalon Peninsula causing major flooding in St. John’s and it was declared as “the worst storm in 100 years”. Again in September 2003, this time in Halifax, a category 2 hurricane known as Juan moved directly north and caused major damage across Nova Scotia, New Brunswick, and Prince Edward Island. Hurricane Juan was so severe that the World Meteorological Organization retired the name Juan from the list of potential hurricane names – the first time ever that a name was retired from a storm doing damage on Canadian soil. What was once thought to be a problem for those living in the Caribbean, hurricanes are now beginning to be taken very seriously in Atlantic Canada.
For hurricanes to form the sea surface temperature beneath the formation must be at least 26.5°C or warmer. Hurricanes begin as tropical disturbances as they begin to become organized and form into larger, more destructive systems. The minimum classification for this is 24 hours as they continue to intensify into tropical depressions. Tropical depressions are already capable of producing heavy rainfall and sustained surface winds between 37 and 62 km/h. Once winds of 63 km/h have been reached, tropical depressions are upgraded to tropical storms and given a name. Not all tropical depressions or tropical storms become hurricanes, but if the right oceanic and atmospheric conditions are present they can grow into massive hurricanes.
When surface winds reach 118 km/h, tropical storms become official hurricanes. Hurricanes are divided into 5 categories via the Saffir-Simpson scale shown below.

Category Wind Speed (km/h) Storm surge (meters) Description
1 118 - 153 1.2 little damage
2 154 - 177 1.8 damage to shrubbery, mobile homes, small craft
3 178 - 210 2.7 damage to trees, roofs, mobile homes, some flooding
4 211 - 249 4.0 damage to all signs, roofing, major flooding, evacuation
5 249+ 5.5+ major damage to vegetation, buildings, complete building failure, massive evacuation


The most powerful winds and heaviest rainfall produced by a hurricane or tropical system are in the northeast quadrant. Other negative effects are hail, torrential rains, thunder, waterspouts, and tornadoes. The storm surge is the difference in ocean water level between the predicted astronomical tide and the actual observed water level, resulting in high water levels that the hurricane generates along coast lines. The 'eye' or center of the storm is the point of the lowest barometric pressure and can usually be seen on RADAR images and satellite images. The strongest winds are around the eye known as the 'eyewall'. Inside the eye are the calmest parts of the storm, sometimes infact clear sky can be seen but this is only a temporary calming as the backside of the hurricane will pass by as well.
This image is of Hurricane Dennis about to hit Pensacola, Florida on 10 July 2005 as a category 3 hurricane.




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 Last Modified: 06 June 2007 - 20:55 GMT
Page URL: http://www.oocities.org/meteogilmore/summerwa.htm

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