vorticity

Tropical Storm Colin

Invest 91L was reclassified as Tropical Depression Four yesterday morning and at 5:00 am today it became the third tropical storm of the season – Colin.

Although it is a tropical storm, it is very small in size. It is also very ragged in appearance. The SST’s in the area of TS Colin are in the 28° – 29° (C) range which is plenty enough for continued development but Colin’s biggest negative is the storm’s size. It makes Colin vulnerable to any mid to upper increases in either dry air entrainment or wind shear. There is some SAL but it is to the northwest of TS Colin and it is not affecting the storm right now.

Currently, TS Colin looks very sickly due to some westerly vertical shear along with the rapid forward motion (24 MPH). There is also a question whether Colin has a closed circulation or not. It is a must for a tropical cyclone to have a closed center of circulation other wise it will be downgraded to an open wave.

The forecast (short term) is fairly simple. If Colin survives the day and/or can find a way to he must do it quickly. The next 24 – 36 hours are crucial for any further development. Beyond that time frame, Colin will start to encounter an increase in the upper level winds caused by a western Atlantic trough. Any further strengthening is not indicated at this time.

Long term forecast is very difficult. Colin is on the southern side of the low/mid Bermuda high. In 48-72 hours a weakness in that ridge due to mid/upper level near the southeastern coast of the US. This should cause Colin to steer on a WNW pattern and then turn to the the NW as it slows down. At that point, the forecast is very unclear. There is no model consensus at this time. The HWRF and the GFDL models are on the right side of the guidance envelope whereas the Canadian(CMC) and GFDN models are on the left. For this forecast period, the NHC has shifted the track southwest and to the left of the previous model track.

ADDENDUM:
As expected, Colin did not last long. As of 5:00pm the NHC dropped Colin from as TS to a remnant low and no longer putting out any advisories unless regeneration occurs. There is still a lot of vorticity so regeneration may happen in a 2-3 days.

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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.

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