Re: The difference between layers
Posted by
Stedwoo on 8/28/2012, 2:59 am
A hurricane is typically steered by the winds in the 850mb (5,000 ft high) to 200mb (35,000 ft high) range of the atmosphere with the strength of a hurricane having some effect of the level of steering winds that influence it. Having said that do not confuse the pressure of a hurricane with the steering level to view in order to try and anticipate where a storm is going. A good measure to look at for an average is 500mb as that is typically the average of the upper and lower level of the atmosphere. When you do have a layer (height)going in a different direction you end up with sheer.
The most important things to look at when look at when looking at the steering column is the two key things that steer a Hurricane, the Coriolis effect (and object rotating counter clockwise always deflects to the right) and a hurricane goes to the weakest spot in the atmosphere.
This means that once a tropical wave become cyclonic and spins counter clockwise it wants to go to the right. However if the pressure to the right of it, North, is higher than to the left it then the hurricane goes west until it finds a weakness that allows it to go right.
The primary weather feature that prevents Hurricanes from going north in the Atlantic is the Bermuda high that typically builds in the middle of the Atlantic this time of year (currently 29 N and 55 W) and while its center moves east and west it also gets stronger and weaker at various times. As you get farther from the center of the high the pressure gets lower and at some point the pressure is weak enough for it to go north. In the case of Isaac the weakest point between the Bermuda high and the High centered over Colorado and Kansas area is the Mississippi River area. However it appears the weakness has been weak enough to allow some winds from the north to come down and sheer it on the NE side and keep it from strengthening. Also some of outer band got grabbed by those winds ( a hurricane influences steering currents about 5 degrees or 300 miles avg out) and pulled them off to the east. That is what cause all the flooding here in Palm Beach county as the band came back east while the storm went west.
I know this is much simpler and basic than you needed or asked for but I know with Isaac headed towards the Gulf Coast we have some new ones around and thought I would keep it at a basic level.
PS if I made any errors all please feel free to correct.
Stedwoo
|
138
In this thread:
Sheer forcast -
Shalista,
8/27/2012, 11:08 pm Post A Reply
This thread has been archived and can no longer receive replies.