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Something Is Brewing In The Gulf Of Mexico - Where Do Hurricanes Form In July?

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The National Hurricane Center is currently watching a weather system closely. As I wrote over the weekend in Forbes, a low pressure system is spinning its way from the U.S. mainland to the Gulf of Mexico. Forecasters give it an 80% chance of development by the end of the week. Anyone living along the Gulf coast from Texas to Florida should pay close attention to this evolving system. Whether it becomes a tropical depression or a hurricane, it will be a significant rainmaker in that region. As my meteorological peers and I watch the odd progression of this system, I thought that it would be useful to answer the question, "Where do hurricanes form in July?"

Tropical Tidbits website

Before I grab my meteorologist "hat" and answer that question, I should be a responsible journalist and provide the latest update on the current system. According to The National Hurricane Center and its 8 am Tropical Weather Outlook issued on July 8th :

A trough of low pressure located over central Georgia is forecast to move southward toward the northeastern Gulf of Mexico, where a broad area of low pressure is expected to form in a couple of days. Some gradual development is possible thereafter and a tropical depression is likely to form by the end of the week while the low meanders near the northern Gulf Coast. Regardless of development, this system has the potential to produce heavy rainfall along portions of the northern and eastern U.S. Gulf Coast later this week.

NOAA

It is too early to determine which model scenario is most likely to play out, but the European model (graphic above) has been consistently bullish on development. It also moves the storm gradually into the western Gulf of Mexico. National Hurricane Center meteorologist Eric Blake tweeted Monday morning,

Remarkably up to 80% now. This type of model forecast unthinkable even a decade ago- an accurate genesis fcst from a MCV that originated over the Rocky mountains!

He is right. While we have seen tropical systems develop from mesoscale convective vortices over land before (see aforementioned Forbes article for an explanation), the level of progress of the weather models to sniff out such meteorological complexity so far in advance is impressive.

Is this potential storm likely to form in a place that we would expect them to in July? The answer is yes. If you review tropical cyclone origin points (graphic above) during the period of July 1st to July 10th (data is from 1851 to 2015), there is a cluster of points in the Gulf of Mexico. Other favored regions of development in July included the eastern Pacific Ocean and the far western Atlantic Ocean. As the season advances, the origin points tend to shift into the Atlantic and Cape Verde region off the coast of Africa. According to the WeatherBug website:

July can be the “ramp up” period to the busiest part of the hurricane season later in the summer.....On average, by the end of July, two named storms will form in the Atlantic Hurricane Basin....This would mean that in an average hurricane season, approximately one-fifth of the named storms stem from July’s activity.

In July, the water temperatures are often sufficiently warm in those favored regions to support tropical development if the wind shear (changes in wind speed or direction with altitude) is not disruptive. Water temperatures in the Gulf of Mexico are currently well above the 80 degree F threshold, and upper-level wind conditions may also be favorable later in the week.

NOAA and Rutgers Marine Lab

Michael Lowry, a hurricane expert now with FEMA, tweeted the graphic below showing where hurricanes have made landfall from 1966 to 2018. He also points out that these storms were not always big "windmakers" but often produced prolific rainfall. I am so glad that he makes this point because the rainfall hazard from tropical systems is often not "feared," "covered," or "emphasized" as much as the wind or storm surge aspects. With recent storms like Harvey and Florence, I hope the public will become more savvy consumers of the total impact potential of tropical systems rather than category. Even if this storm never becomes "Barry" in name, there will be impacts.

Michael Lowry

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