Leslie Slowly Organizes; Michael Strengthens
Surprisingly for the beginning of September, the Atlantic is the only basin in the world with an active tropical cyclone, as the East Pacific lost John today and the West Pacific continues through an unusual calm spell for this time of year. The Atlantic actually has two storms being watched tonight, with the biggest threat being Tropical Storm Leslie. As of the latest (5PM) advisory from the National Hurricane Center, Leslie has maximum 1 minute sustained winds of 65mph and a minimum central pressure of 994mb. Leslie is currently located about 500 miles SSE of Bermuda and is creeping north at just 3mph.
Forecast for Leslie
Leslie's life so far has been dominated by shear, as convection has been repeatedly blown off the center, leaving it exposed. That has changed some today though, as an area of convection has been able to persist over the center. Despite this, Leslie remains in an area of moderate shear of about 20kts, and significant strengthening is unlikely for the next 2 days. After this time, however, shear will relax, and conditions will become much more conducive for development. Because of this, the NHC is forecasting Leslie to be a Category 2 hurricane with 105mph winds in 5 days. One possible variable in the intensification process will be Leslie's extremely slow motion. Slow moving storms tend to cause cold water from deep in the ocean to come to the surface in a process known as upwelling. These cooler waters can act to weaken a tropical cyclone. I do not feel this will be much of a problem, however, and neither does the NHC as they have noted the high ocean heat content in Leslie's area should limit affects of upwelling. I generally agree with the NHC intensity forecast, as it appears strengthening should begin in about 48 hours as they suggest. The track forecast continues to have a degree of uncertainty, but the models have come into decent agreement. The biggest concern for land remains the island of Bermuda, as the official NHC forecast puts the island in the right front quadrant of a strengthening hurricane in 4-5 days. I do not feel impacts will be too severe on the island for a couple of reasons. One is that most buildings in Bermuda are built very well. Another is that it appears Leslie will be rapidly accelerating as it passes by the island. Still, residents there should definitely heed any advice given by emergency management agencies. Large waves and beach erosion will likely be the biggest threats. After it passes Bermuda, Leslie will likely continue a NNW movement before turning N and eventually NE as a trough picks up the storm. Right now direct impacts on the United States East Coast appear very unlikely, but high waves and dangerous rip currents will be major concerns, and residents of the East Coast should avoid the water this week. There are some indications that Leslie will become a very powerful extratropical storm after it loses tropical characteristics. It will be an interesting event to watch for sure.
Figure 1: Official NHC forecast for Leslie.
Figure 2: Tropical Storm Leslie.
Michael Strengthens, No Threat To Land
In the open waters of the Atlantic, tiny Tropical Storm Michael has become better organized today. As of the latest advisory from the National Hurricane Center, Michael has maximum 1 minute sustained winds of 50mph and a minimum central pressure of 1006mb. It is moving NNW at 7mph. Michael has strengthened today as a mid level eye has been evident on microwave images and occasionally on satellite images.
Figure 3: Microwave image of Michael.
Forecast For Michael
The latest NHC intensity forecast brings Michael to 70mph in 4 days. Michael is an extremely tiny cyclone, so there is a large bust potential both ways with the intensity forecast. Small storms like this are usually very vulnerable to any unfavorable conditions, and a sudden increase in shear could easily tear up the system and cause dissipation in the next 5 days. On the other hand, small systems like this can spin up very quickly under the right conditions, and Michael could become a hurricane if this happens. I'm leaning more towards the aggressive solution as I am forecasting Michael to peak at around 80mph. Regardless, Michael is not a threat to land.
Figure 4: Official NHC forecast path for Michael.
Just a quick side note: I (like many of us) am back in school so I won't be on before 3PM most weekdays for the next several months. I may not have time to make many blogs either but I will try to get them out when necessary.
Thank you for reading, have a great night!