A hurricane, a tropical storm, and three areas of interest pepper the Atlantic

Today's post features Tropical Storm Helene, Hurricane Isaac, and what could be the next three named storms scattered all over the Atlantic.

First, Helene rapidly intensified on Thursday at an impressive rate.  Peak winds increased from 85 mph on Wednesday night to 140 mph on Thursday night, and amazingly, from 105 mph on Thursday morning at 11am to that 140 mph just twelve hours later.  To qualify for the conventional definition of "rapid intensification", the intensity needs to increase by at least 35 mph in a 24 hour period... Helene did that in just 12 hours.  The infrared satellite animation below spans 3am through midnight EDT on Thursday.

This is not only the fourth hurricane landfall on the US Gulf coast already this year, it was the most intense hurricane to ever make landfall in the Big Bend area of Florida.  The storm's huge expanse of strong winds helped it to generate record-breaking storm surges along the west coast of the Florida peninsula, and almost certainly the Big Bend area too (official numbers take time to get because ground crews need to carefully survey high water marks over a large area, sometimes in remote or hard-to-reach locations).

As expected, strong winds punched far inland, and as I write this the damage is still unfolding and being discovered.  Now that it has made landfall, it will rapidly lose its tropical characteristics, but it doesn't go away... there are still a couple days of trouble ahead in the form of flooding rains and multiple tornadoes.

Early Friday morning, Isaac was upgraded to the season's 6th hurricane and is still located in the far north-central Atlantic.  The NHC forecast is shown below... it now indicates that Isaac will stay rather far to the northwest of the Azores late this weekend.

Next, the African easterly wave I mentioned in the deep tropics east of the Lesser Antilles (Invest 98L) is extremely close to becoming the next tropical cyclone this season.  It could be upgraded to Tropical Depression 11 or even Tropical Storm Joyce any time today.  It is still very likely going to turn north into the central Atlantic well before reaching the Lesser Antilles, so no threat to land.

While on the topic of easterly waves, the yellow area we see in the overview at the top of the post is the next wave that has a low chance of developing in the coming week, so for now, I won't go into detail on it.  The wave just left the African coast yesterday.

Then, the area highlighted over the western Caribbean has a 30% chance of development in the coming week, according to NHC.  Model ensemble forecasts are very hazy on the long-term future of it, but for now, it's something the Yucatan peninsula and the Gulf coasts of Mexico and the US will want to pay attention to in the coming week.

Finally, here's an update on the overall activity so far this season.  We have now had 9 named storms, 6 hurricanes, and 2 major hurricanes.  The average by this date is 10, 5, and 2.

In terms of Accumulated Cyclone Energy, after an explosive start, the season at just 78% of average for the date.  

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