The North Atlantic Tropics Looking to become Active Again This Weekend or Next Week

It’s August and with that it’s time for the North Atlantic to show its tropical cyclone “muscle”. Tropical waves become more numerous as mesoscale convective systems form over the tropics of West Africa and race off into the open Atlantic; their mid-level “vorticity” or spin the seed for possible further development. The National Hurricane Center in Miami has pegged one Thursday with an 80% chance of development between now and Tuesday (40% chance between now and Saturday).

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Shortwave infrared image (sometimes known as “nighttime visible”) taken at 8 pm EDT Thursday. This shows a cloud mass moving off West Africa associated with a new tropical wave south of the Cape Verde Islands. (NOAA)

Mid-range models suggest the system will develop possibly into a depression or tropical storm, moving generally westward toward the Lesser Antilles heading toward Tuesday. Much more on what will happen will depend on the system’s development. Mid-level dry air brought in from the Sahara Desert will be an issue for this system as it approaches the Lesser Antilles if it moves north of 15N. As far as upper-level winds, forecast shows a modestly favorable environment for development, but details will wait until down the road. Water temperatures in this part of the Atlantic – known as the Main Development Region (MDR) – are running up to 1.5 C (~3 F) above average with abundant warm sea surface temperatures above 26 C (79 F) west of 35 W.

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Current Sea Surface Temperatures over the tropical Atlantic Ocean. The orange-red and red shades indicate temps at and above 26 degrees C. (Wunderground.com)

Because of the strong semi-permanent “Bermuda High” expected to dominate the Central and Western Atlantic next week, this system will need to be watched by interests in the Western Atlantic Basin for potential impacts in case it does not curve northeastward out to sea because of the subtropical high pressure system to its north (assuming it develops).

Also of interest is a system in the Eastern Caribbean Sea. It is in a more hostile environment (shear and dry air main problems) and only has a 40% chance of development over the next 5 days.

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Shortwave IR image at 8:45 pm EDT showing generally disorganized thunderstorm activity associated with a tropical wave in the Eastern Caribbean. (NOAA)

The Atlantic has been running about a month ahead of schedule on named storms, but has been dead quiet on hurricanes. The 1966-2009 average for the first hurricane in the basin is coming up (August 10th), but given recent years of activity, the Accumulated Cyclone Energy (ACE) thru Aug. 2nd is running at its lowest level in the basin since 2009. But still 90% of the ACE on average occurs from here on out, so much can still happen, especially given the lack of one otherwise major hindering presence in El-Nino.

I’ll keep track of these disturbances in the coming days and have more for you if they develop into organized systems. Stay tuned!

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Tropical Storm Emily impacting much of Florida Monday

Tropical Storm Emily formed last night over the eastern Gulf of Mexico.  An area of low pressure developed thunderstorm activity which managed to consolidate and organize as it approached the central gulf coast of Florida overnight. Meteorologists began to notice the increasing organization of the system on local radar and at 6 am EDT this morning, the National Hurricane Center in Miami declared the system “Emily”.

Regional radar showing huge rain extent associated with Emily near and south of the center.
Enhanced infrared image showing cloud temperatures of Emily. Coldest temps (reds) near center along central gulf coast.
 

As an upper atmospheric trough of low pressure digs southeastward from the upper-Midwest over the next 2-3 days, this is expected to steer Emily northeastward. It will move out of Florida by overnight tonight/early Tue and head off into the open waters of the Atlantic well-offshore the East Coast. Land interaction today will weaken it but it may regain some strength over the waters of the Gulf Stream mid-week.

Atlantic tropical cyclone statistics thus far this season: 5 named storms, 0 hurricanes, 0 major hurricanes. On July 31st, on average the Atlantic is expected (based on 1966-2009 data) to have observed only 1 named storm, 0 hurricanes, 0 major hurricanes (on Aug 1st, the average named storms increases to 2). As we go deeper into the month of August expect the hurricane numbers to go up thanks to favorable below average wind shear and above normal oceanic heat content currently in existence in the Main Development Region (MDR) of the Tropical Atlantic. 


This area is largely turned off in earlier months but ramps ups later in the season as tropical waves develop from the tropics of West Africa and moves south and west of the Cape Verde Islands. So the Atlantic still has a lot left in the tank as far as heat energy to release.