Monthly Archives: June 2010

Invest 93L

Starting yesterday, a system was beginning to catch the eyes of those who are interested in the tropical weather. A modest to strong region of very intense thunderstorms that are in the Caribbean are beginning to look like that we may soon have the first tropical depression (at least in the Atlantic basin). Wind shear in the area is very low, the SST’s are very warm – 29 to 30 degrees Celsius. The MJO (Madden-Julian Oscillation) also does seem to favor tropical development. It is now in the wet-phase over that region. One negative side is there has not been a lot of spin according to the University of Wisconsin 850 mb relative vorticity analysis. 93L will probably begin to get an increased inflow from low level air and help the development of the spin soon.

At this time the NHC is calling for a 40% chance of developing of into a tropical depression. I wouldn’t see that until at least Wednesday maybe even Thursday. The GFS, NOGAPS, and UKMET models have been very reluctant to develop 93L for the time being. The GFDL model is expecting 93L to be a weak tropical storm in the next 5 days. At this time – the GFDL has been flip-flopping so lets just see what happens.

One worry is the possible flooding in Haiti. Any mudslides then there will be some unfortunate deaths. Lets just pray this will not be the case. Haiti has had enough over the past couple years.

As always – please use the NHC or your local weather for official information.


Weather or Knot

Using a play on words the name of this blog just worked out perfectly. Since both the blog and the forum are based mostly for the world of weather (meteorology). The name of the main weather site but the blog is

I am sure one of the first question to be asked is what is the coriolis effect. That is a great question! In physics, the Coriolis effect is an apparent deflection of moving objects when they are viewed from a rotating reference frame. Unless you are a meteorologist or a scientist – it probably is nothing but word a bunch of words but no meaning.

In Meteorology, perhaps the most important instance of the Coriolis effect is in the large-scale dynamics of the oceans and the atmosphere. In meteorology and ocean science, it is convenient to use a rotating frame of reference where the Earth is stationary. The fictitious centrifugal and Coriolis forces must then be introduced. High pressure systems rotate in a direction such that the Coriolis force will be directed radially inwards, and nearly balanced by the outwardly radial pressure gradient. This direction is clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. Low pressure systems rotate in the opposite direction, so that the Coriolis force is directed radially outward and nearly balances an inwardly radial pressure gradient. In each case a slight imbalance between the Coriolis force and the pressure gradient accounts for the radially inward acceleration of the system’s circular motion.

Hopefully using an animation might give you a clearer idea of what the coriolis efffect is:

Now there still is the myth about the direction of rotation in a bathtub or toilet and that the Coriolis Effect was the cause. While theoretically the Coriolis Effect might affect the draining flow, it is stronger other factors (temperature distribution, turbulence and wall shape) that dominate.