Two potential hurricanes

After a spate of almost storms, we now have two systems that seem to have the potential to become full blown tropical cyclones. In the Atlantic, tropical depression eighteen has emerged from the dust off of Africa and is expected to become Tropical Storm Sam later today. Conditions are favorable for strengthening, and it is expected to become a hurricane and probably reach category three intensity by this weekend …

click to embiggen.

I’ve had reports that this storm is being hyped by the usual suspects. It’s way too early to get excited about it. NHC doesn’t even have a “key messages” product yet, there are no watches or warnings, and the advisories don’t have the “magic words” in them (“Interests <somewhere> should <do something”). So worrying about it is a waste of energy.

Those who follow the blog know that once NHC starts advisories I rarely show the “spaghetti maps” of track models. The reason is that interpreting these tracks takes a deep understanding of each model, the synoptic situation, and many other factors. They aren’t all created equal,and what is a “good” model today can be a “bad” model tomorrow and vice versa. By far the majority of people (even meteorologists) who babble on about this or that model are wasting your time and trying to keep your eyes on their screen (and of course their blipverts). The models are guidance – not a forecast – and most of the time it is a distraction to show them and focus on every wobble or change. What matters are the trends and patterns – rarely the specifics. Another issue is that the official forecast only goes out five days – for good reason. Beyond that the forecasts are so uncertain as to be confusing, and the risk of over-reacting and disrupting people’s lives for no good reason is quite high. That said, showing them can be useful for context and explaining the uncertainty and difficulty of the official forecast (or lack thereof). Here is a selection of the major track models for TD20 along with the official forecast.

The purple lines skirting the Leeward Islands an headed into the Bahamas is the European Center Model (ECM) and ECM Ensemble Mean (EEMN). The blue line is the US Global Forecast System (GFS). These two scenarios illustrate the danger of focusing on models, especially beyond five days. One would be a source of concern; the other (GFS) a fish storm, similar to most of the tracks this year. Which is most likely? I think a turn away from the US is more likely at this point given conditions this year, but it’s way too early to get excited about it one way or another. If you have a hurricane plan, nothing to do at this point.

In the West Pacific, Tropical Depression Twenty should become Tropical Storm Mindulle today, and later today (tomorrow Guam/Japan time) a Typhoon. It too is forecast to intensify to category three or four intensity – a “super typhoon”. While it is over Guam at the moment, it will be well past the islands before it intensifies. Here’s the latest Joint Typhoon Forecast Center track …

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