Misconceptions about patterns

[MiamiensisWx]

In 2007, I have heard numerous posters stating that Olga (and other systems) would have hit Central America if we were in the peak months. Well, I couldn't disagree more strongly, and I'll present evidence to support my position. It seems like more posters (than ever witnessed) have misconceptions about patterns and pattern changes, and that could be dangerous for the general public. Here is my opinion.

It all depends on the synoptic setup. First, you must consider the situation (i.e. whether a TC is well developed). Well developed, deep tropical cyclones are steered by the upper levels (usually <500 mb). If Dean and Felix were weaker systems, they would have been steered by the low-level (850 mb) flow, even if the 500 mb ridging was weaker and supported a northward turn. Additionally, weak sfc fronts, upper lows, tropical upper tropospheric troughs, and continental shortwaves regularly alter the pattern. It depends on timing. For example, Charley was a well developed TC when it passed Jamaica, thus it was affected by the UL pattern (<500 mb). An UL trough (s/w) was moving over FL, thus weakening the UL ridge and allowing Charley's northward turn across Cuba.

I think it is dangerous (from a citizen and meteorological standpoint) to assume that things would trend in a particular direction (i.e. repeat in summer) because of the outcome via one pattern during a few days in a single year (in a single occurrence). If Felix and Dean arrived a few days earlier or later than anticipated, the outcome could have been much different. Heck, it could have been much different if the UL pattern was different at the time.

Every situation is different, regardless of the time during a year.

Key points:

1) Numerous small factors can affect the track of a TC, regardless of the time during a year. A TC can move in any direction throughout the year. Although the formation point (i.e. E Atlantic, Caribbean, N Atlantic, GOM, etc.) can be a useful tool in general climatology, a system's path ultimately depends on the pattern that is present when the TC exists. An October system in the Caribbean does not guarantee a Wilma-type track. Climatology also indicates several systems have continued westward into Central America or Mexico. Case 1: Iris 2001. Some late season tropical cyclones formed in the Bay of Campeche and moved south. Case 2: Larry 2003. Some dissipated. Martha 1969 even made landfall in Panama because of its far southern formation.
2) Climatology is highly misunderstood. People tend to utilize "climatology" in the wrong situations (i.e. a TC cannot strike this location). Climatology is a compilation of historical data, including past storms, tracks, and numbers during each season. These sets of data can be utilized to find averages, plot general spawning regions for storms, and plausible general tracks during each month of the season. Climatology should not be used to determine individual storm intensities or landfall points. It can be used to determine plausible paths. Climatological data is useful, but people utilize climatology as absolutes. That defeats the purpose of climatology.

[Sanibel]

I think Olga is doing the climatologically expected right now and hook turning north.

You must admit we saw three rather flat-west tracks in the Caribbean - which should be noted.

[jinftl]

Given the level of analysis that goes into the science of forecasting each and every storm, I don't see the forecasting community letting its guard down, assuming a storm will follow the path of earlier ones.

[Ptarmigan]

You raise some good points. Lot of things affect where TC will go. Storms aren't going to care about climatology. One can use history, but there is no guarantees where it will go. As for Olga, I would expect it take that path at this time of the year. I have never heard of any storm in December forming the Gulf of Mexico or heading into that area. Maybe it happened before 1851. I don't know.