Halfway Through The 2012 Season
It's hard to believe, but we are halfway through the 2012 Atlantic Hurricane Season. I'll have more about that later on in this post. First though, there are some very active tropics to get to, as would be expected near the climatological peak of hurricane season. There are currently three areas of interest in the Atlantic. The biggest threat right now is Tropical Storm Lesile. As of the 11AM EDT advisory from the National Hurricane Center, Leslie is located nearly 300 miles north of the Leeward Islands, and is moving NW at 15mph. Leslie currently has maximum sustained winds of 65mph, and a minimum central pressure of 997mb.
Forecast for Leslie
Leslie is an extremely sheared tropical cyclone, as evident by nearly all of the heavy thunderstorm activity being located to the south of the center, as seen in Figure 1.
Figure 1: Tropical Storm Leslie. Shear is evident as the center can be seen to the north and west of the strongest convection.
Leslie is also fighting a dry environment. Due to these unfavorable conditions, strengthening is unlikely for the next 3-4 days, as the official forecast shows Leslie weakening slightly in that time. It wouldn't surprise me if it weakened more than indicated as conditions just won't be favorable at all for tropical cyclones. Beyond 4 days, however, it appears shear will relax and give Leslie an opportunity to strengthen, and the official forecast from the NHC indicates Leslie will be a minimal hurricane in 5 days. The track forecast for the next 5 days keeps Leslie moving NW for the next day or so, followed by a NNW and then N turn, possibly followed by a bend back towards the NW in 4-5 days. It should be noted that Leslie is not expected to move much during this time period, as it will likely slow down tomorrow. What happens beyond 5 days, both with track and intensity, is uncertain. The most immediate issue will be the island of Bermuda, as it looks like it will be in the future path of Leslie. By the time it gets to this point, Leslie may have intensified quite a bit, as several models are indicating, so anyone in Bermuda should be monitoring the situation. It is too early to determine any possible impacts on the United States, but most indications are that Leslie will stay offshore and only provide some large ocean swells.
Figure 2: Official NHC track forecast for Leslie.
As would be expected of a system in Kirk's location, he is weakening and accelerating. His circulation has become elongated, and he will likely dissipate soon. Kirk currently has maximum sustained winds of 50mph and a minimum central pressure of 1002mb as he races NE. Kirk is not a threat to land.
Figure 3: Tropical Storm Kirk, rapidly being swept away towards the NE.
Invest 99L Little Threat
In the open waters of the central Atlantic, an area of disturbed weather, Invest 99L, is being watched for development by the NHC. In their latest Tropical Weather Outlook, they gave the disturbance just a 10% chance of development in the next 48 hours as environmental conditions are not conducive for development. I would put these odds slightly higher at about 25% since these small systems have a tendency to spin up unexpectedly. Regardless, 99L is no threat to land.
Figure 4: Invest 99L, showing a tight circulation but little convection.
East Pacific Remains Active
Former Hurricane Ileana dissipated today over cool waters, with nothing left of her except a convectionless swirl. This remnant circulation should dissipate in the next few days and it will not threaten any land areas.
Figure 5: Remnant low of Ileana.
The next potential system in the East Pacific is located about 350 miles SSE of Baja California. This disturbance, Invest 99E, is moving WNW at about 15mph. It is being given a 90% chance of development in the next 48 hours, and I agree with this percentage. 99E's WNW motion means it is heading away from the coast of Mexico, so it should not be a threat to land.
Figure 6: Invest 99E. It is a very large disturbance so it may need to consolidate a bit more before being classified.
Halfway Through the Season
Three months down, three to go. We are now halfway through this year's Atlantic Hurricane Season. This season has been similar to last season in some ways- a very large number of named storm, but several of them being weak and no threat to land, but with one big hit on the United States. Last year it was Hurricane Irene, and this year it was Hurricane Isaac. Both were category 1's at landfall, but both were very large storms that provided impacts greater than a normal storm of their category. 2012 has featured two storms that formed before the official start of the season (Alberto and Beryl) and has been one of the most active years on record in terms of named storms. We've seen one of the greatest forecasting challenges of all time (Debby) as well as a near major hurricane near the Azores (Gordon). The theme of the year so far has been dry air, as several storms, including Isaac, struggled with this issue.
What to Expect for the Rest of the Season
We are nearly to the climatological peak of hurricane season; it will occur in about a week. Early this season, predictions were for an abrupt shutdown to the season by early to mid October as a predicted El Nino set in. The El Nino has been very slow to develop, however, and may never develop at all, though effects from the warmer than normal Pacific waters have been evident in our basin. This delayed El Nino likely means that while activity should slow down significantly by October, the season should not completely shut down and we could see 2-4 storms between October and November. Throw in about 4 storms in September and we could be looking at a grand total of nearly 20 storms, much higher than originally predicted, though some have been rather pathetic and short lived. As always, it is impossible to pinpoint any potential land impacts, so the best thing to do is keep an eye on whatever forms.
Thank you for reading, and have a happy Labor Day!