Week 6: Tropical Quadrants

Here in Week 6 of Tropic Topics, meteorologists Kristen Kennedy and Grace Thornton are accessing the signals of suppression still inhibiting tropical activity along the equator.

During this week’s discussion, the main inhibitor is Saharan dust, which we have seen throughout the summer season already. However, there was one area of interest sitting off the coast of the Mid Atlantic, but only had a 10% chance of development. Gulf water temperatures increased by about 1-2 degrees from the last week, which is one factor that would actually aid in development heading into the tropical season.

The peak of the tropical season begins its uptick during late July and remains elevated through late October. During week 6, the team goes over three general areas where tropical development occurs during this stage in the season. Situation A stretches from the southern Caribbean towards the Gulf Coast of the USA. If an area of interest develops from this area, it will usually happen due to the initialization of a Central American Gyre (broad area of rotation across Central America), and then gets pulled northward. These storms can organize rapidly as they are already in warm waters, but dust and shear are a hindrance at the moment. Situation B, overviews tropical activity forming in the equatorial Atlantic off of West Africa. These storms usually ride the easterly trade winds around the Atlantic’s sub-tropical high and end up riding over the Bahama’s and Southeast coast. Situation C is the development region in the Central Atlantic and Eastern Caribbean relating to tropical waves off of northeastern South America. It is not the most common area, but still possible.

Next, the team breaks down the quadrants of a tropical system, this includes the NW, SW, SE, NE quadrants, and the eye of any given storm. The greatest things to note are that the NE quadrant is the most impactful part of the storm relative to the SE side, which is the least impactful. The NE side is the area that includes the storm’s forward motion, which in turn imposes heavier impacts in regards to wind, rain, surge, and tornadoes. In the NW section flooding is the major concern, while winds are usually the slowest. In the SE section, both flooding and tornadoes are the largest concern, due to the dry air that wraps underneath a rotating tropical system. The SW section, while it still can be impactful, is the least strong part of any given storm.

There are historical storm situations where the quadrants obviously played a major role. Hurricane Katrina, Harvey, and Ivan are the three scenarios the team digest. During Katrina, while New Orleans was within the NW quadrant, which is not the strongest, it still retained detrimental flooding and surge. This is due to the geographical position of Lake Pontchartrain, which sits just north of the city. Southwesterly winds across the area pushed surge from the lake across New Orleans, while additional heavy rain added to flooding. The next storm came ashore closer to home, Hurricane Ivan. The Florida Panhandle was on the eastern side of this storm, where it experienced tons of moisture and many confirmed tornadoes, as dry are filtered in from the SE. During Harvey, the storm’s first landfall over Rockport, TX recorded extremely strong winds speeds within both the eastern quadrants of the storm. Harvey meandered back into the Gulf after its initial landfall, and slowly moved northeast along the coast of TX, eventually making landfall in lower Louisiana. The series of days it was lingering offshore, Houston remained within the two north quadrants, meaning that they were bearded with heavy rain and wind for almost 4 days. This lead to over 3 ft of rainfall in Houston and its surrounding areas.

Week 5: Elsa Wrap-Up

Elsa made landfall in Taylor County Florida, where it caused expected amounts of storm surge, flooding, and a few tornadoes moving northeast into southern Georgia/South Carolina. At the time, Elsa was moving northeast at 20 mph with max sustained winds at 45 mph. Areas surrounding the Chesapeake Bay were concerned about flooding, wind, and rough waters. 

Apart from Elsa, the rest of the tropics were relatively quiet. The subtropical high and Saharan Air Layer over took much of the equatorial atmosphere, causing suppression for most of the convection out there. Another suppressive factor has to do with the stage of the Madden-Julian Oscillation, which was supporting divergence of winds, as well as high pressure at the time. Basically meaning, any tropical wave making its way towards the Caribbean would be inhibited from further development. The suppressive phase is forecast to continue for a few more weeks, keeping the tropics quieter through the beginning of August. Taking a step back, we were previously in an enhanced phase of the MJO throughout June/early July, which supported greater tropical activity. This helped form Claudette and Elsa. 

The rest of the Storm Teams’ Tropic Topic episodes will include a segment where we judge the best hashtags for storm names our viewers can come up with. Submit yours during any episode of the show by commenting. Viewers can also message their submissions to Ross, Kristin, and Grace on their social media pages at any time.  

Week 4: Keeping an Eye on Elsa

This week, the First Alert Storm team broke down what was Tropical Storm Elsa. The first thing to note is that Elsa had a nice structure on satellite and was moving very quickly. The fast movement is not as favorable for intensification, as it’s harder for the tropical storm to keep its vertical column upright for long. Looking at the track published from the National Hurricane Center at the time, it is noted that the forecast cone is quite small heading into the next 3 days. This is due to high confidence that Elsa was headed just under Cuba and towards the eastern Gulf. The cone expands wider as forecast confidence lowers towards the beginning of the next week. At the time, the Florida Panhandle was expected to stay on the west side of the storm, which would result in drier conditions, and little to no impact in Panama City. Although this forecast did eventually verify, with Elsa making it’s second landfall in Taylor County. It is important to note that this doesn’t happen for every storm. Forecasts 5-7 days out, like this one, don’t always have as much accuracy and usually change. Start to pay attention to the forecast at least 3 days out. By that time, meteorologists have a much better idea of when and where the storm will make landfall.

Elsa was unable to reach higher than Category 1 strength due to a few inhibiting factors. The first, was dry air being ingested from the Saharan air layer. Intensification of Elsa would have needed more moisture in the surrounding atmosphere. The second, was the fast forward motion from the easterly trade winds, without the presence of low shear on the west side. Third, was the interaction with Cuba that injured the overall structure and strength. 

The team then shifts into the spaghetti model tracks, where they take the audience into possible outcomes of Elsa. Most of the spread curved the storm east, which was good for our forecast at home; but some floated the storm west, where the storm could have packed more of a punch to the Panhandle. These scenarios were mostly dependent on a trough moving in from our west and the placement of the subtropical high in the Atlantic.

Week 3: Breaking Down the Basics

Meteorologist Ross Whitley and Kristen Kennedy are covering some basic ingredients meteorologists look at when deciphering the tropical activity. During this week, the most significant tropical activity afoot was a tropical upper tropospheric trough (TUTT), high wind shear, The Saharan Air Layer (SAL), the easterly trade winds, and the Intertropical Convergence Zone (ITCZ). 

During this week, enhanced satellite shows a lack of tropical activity around our area as the Gulf and Caribbean maintain less than favorable environments. Gulf waters have not warmed enough to provide favorable enough areas for hurricane intensification. Despite this, there are still two areas of interest. The first, sits to the west of the Lesser Antilles. The second, is a wave off the west coast of Africa. 

The area of interest to the east of the Lesser Antilles, is coming into an environment with too much vertical wind shear. Sometimes developing hurricanes will favor light horizontal wind shear, but not in this case. The shear in this case is caused by a tropical upper tropospheric trough, or TUTT. A TUTT is an elevated area of low pressure in the atmosphere at 300 mb (~30,000 ft). An area of low pressure sustained by overall high pressure.The present TUTT is creating a lot of vertical wind shear, which is ripping apart the first area of internet in the Caribbean.

The second area of interest is a tropical wave off the coast of West Africa, that has a 40% chance of development, but may not be far enough from the equator to be swept westward by the easterly trade winds. A tropical wave is a broad area of low pressure that can be enhanced or diminished by other influences in the atmosphere at that time. In this case, if the system was situated more north, the easterly trade winds would potentially help develop the wave into a stronger system. Easterly trade winds are continuous east winds that are apparent all year long by the subtropical high in the Atlantic. These winds shift the tropical waves west into the Caribbean and southern Atlantic for ongoing formation. The system emerged from our main development region (MDR) for tropical waves, the intertropical convergence zone (ITCZ). This area is where the north easterly and south easterly trade winds converge, near the equator. 

During this point of hurricane season, these waves are quite common, but often the rest of the ingredients for hurricanes are not yet strong enough to aid in development; which is what we have observed this week on Tropic Topics.

Week 2: Analyzing Activity in the Gulf

Meteorologist Kristen Kennedy and Meteorologist Grace Thornton discuss the potential development of what would turn out to be Tropical Storm Claudette and its path to the Gulf Coast.

The wave developing off the Bay of Campeche is pushing into the western Gulf of Mexico. It will be steered by wind shear west and a strong ridge of high pressure off the east coast. Across the Panhandle, 2-4 inches of rain are likely to accumulate. There will be an isolated tornado threat with tropical rainbands that move overland on the east/right side of the storm system. Winds should not be significant as the bands impacting northwest Florida will be far from the center of the tropical system.

Week 1: Talking Tropics

Chief Meteorologist Ross Whitley, Meteorologist Kristen Kennedy, and Meteorologist Grace Thornton sit down for a tropical discussion.

Introduction to the weather team that is going to be with you all season long. This season is expected to produce another active season. The forecast is for an above-average number of storms but is not expected to be as active as last year. We go through what the expected number of storms are as well as what June and July typically look like from a storm formation and track perspective.

While this year might end up being an active one we know all too well that the number of storms really doesn’t matter. It only takes one storm to make an impact. Make sure to join the Fist Alert Storm Team all year as we break down week to week what is going on.

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