Well, we did it again. Isaias becomes the earliest “I” storm on record beating out Irene of 2005. In fact, Isaias developed earlier than any eighth named storm prior to the 2020 season. The ninth named storm of the season typically doesn’t develop until Oct. 4. We are more than two months ahead of schedule.
It can be ominous seeing the place you live in the dreaded cone of uncertainty as it is deemed. More on that below. There is no need to panic, but it’s a good time to be extra vigilant. There has been higher degree of uncertainty with this storm because it had not developed a center until late Wednesday evening. Even Thursday morning, the center was not very well defined. Forecasts should begin to improve with Isaias, however, now that there is a developing center.
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A messy storm
First off, Isaias is trying to get its act together, but there is a lot standing in its way. Sloppy has been the theme of Isaias’s life to date. It’s big and moving fast -- two things that are self-detrimental to development. It’s also fighting off dry air and a little bit of wind shear to go with it. There’s also another factor going forward: land.
Hispaniola has some very tall mountains on the southern side of the island. The fact that the storm is large may help it survive the mountainous terrain of Hispaniola. The large, unorganized nature to this point may actually help it in the long run, for one helping it survive land interaction with Hispaniola. If the center was consolidated, the mountains would rip it apart. Bigger, elongated storms like Isaias have a better chance of fighting off unfavorable conditions.
Where’s it going?
Major models are picking up on Isaias staying intact or redeveloping and strengthening after it clears Hispaniola. If it does this it will be good news for us.
The stronger the storm, the better the opportunity it will have to stay off of the East Coast of Florida. In this case, the storm will feel the Bermuda high and get pulled further out to sea or have a close brush with the East Coast of Florida. A weaker storm will tend to move further west, potentially into the eastern Gulf of Mexico.
It seems to me that we will either have a strengthening storm off of the east coast of Florida, leaving inland impacts minimal to none, or a weaker storm moving west of Florida that can enhance a severe weather threat locally, similar to Tropical Storm Cristobal in June. These details will be ironed out after it clears the islands Friday.
I will never say never when it comes to the weather and everyone should be playing close attention as to how Isaias comes together over the coming days. Computer forecasts have been awful to say the least this season in terms of tropical weather and if Isaias finds decently favorable conditions after the islands, it could bulk up into something not seen right now. The asymmetric nature, dry air and wind shear around it, however, should keep it from going bonkers after initially exiting the Caribbean islands.
The cone of uncertainty
The cone represents the probable track of the tropical system. When it comes to the cone, it is important not to focus on the center as the eye of the storm can move within the cone. Impacts are oftentimes felt well beyond the cone as well, so it's important to note that the cone is ONLY forecast the center of the storm.
According to the National Hurricane Center, The cone represents the probable track of the center of a tropical cyclone, and is formed by enclosing the area swept out by a set of circles (not shown) along the forecast track (at 12, 24, 36 hours, etc). The size of each circle is set so that two-thirds of historical official forecast errors over a five-year sample fall within the circle. Based on forecasts over the previous five years, the entire track of the tropical cyclone can be expected to remain within the cone roughly 60-70% of the time.
Over the years, forecasts have gotten better and the cone has gotten thinner, representing relativity less error in the four to five-day forecast.
The Cape Verde season
The locals refer to this archipelago just east of Africa as the Cabo Verde islands. While this season got off to an early start producing Gonzalo, Hanna and Isaias, August officially begins the season where storms become more frequent off of Africa and the dust in the Atlantic becomes less prolific.
This is where the strongest storms of the season typically develop. Meteorologist Candace Campos explains why.
Notice the develop zones expand further east toward Africa .
Looking ahead
As we talked about last week, the African wave train would be active to close out July. Another very juicy wave rolled of Africa a few days and is trying to organize far away from the U.S. Don’t be surprised if we get another depression or storm (or two) to form by the first couple of days of August. If they develop, they shouldn’t last long and shouldn’t be a concern to us.
The MJO, that disturbance that circles the globe through the spring and summer months we often talk about, moves into its unfavorable phase for the Atlantic to start August. Through the middle of August, it appears most of the Atlantic will settle down big time. Now, we can still get storms to develop in an unfavorable pattern, but I would not anticipate a flurry of tropical systems through the middle of August.
By the third and fourth of week of August it may be open season in the tropics. The dust and wind shear in the Atlantic has kept things relatively tame even with all of these storms. That could change in the weeks ahead. Peak hurricane season arrives as we enter September.