UPDATE (Aug 30th)
Irma is a new named storm in the Eastern Atlantic. See this post for details, eventually.
UPDATE (Aug 29th)
There is a system currently raining on Cabo Verde, off the West Coast of Africa (nee Cape Verde) that is expected to develop. It is on the verge of becoming a tropical depression. The National Hurricane Center has estimated that there is a high probability of this stormy feature becoming a tropical storm in a couple of days or so. If it gets a name, it will be Irma, unless some other large rotating wet object takes that name first.
UPDATE (Aug 29th)
How is the Atlantic Season doing so far, in relation to most hurricane seasons?
Using data from NOAA, we can say that on average (using the 1966-2009 baseline) we reach the eight named storm in the Atlantic (Harvey is the eighth) on September 24th. So, we’re having more named storms than average.
This year so far we’ve had 3 hurricanes. Normally one reaches that number of hurricanes on September 9th. That’s a week and a half from now, so we can declare this year a bit above average in this measure, but not spectacularly so.
So far this year we’ve had one major hurricane (Category 3 or above). There are some years with zero major hurricanes, but on average one major hurricane occurs by September 4th. So, we’re close to average now.
UPDATE (Aug 29th)
The following posts discuss various aspects of Harvey
Harvey The Hurricane: Truly Climate Change Enhanced
Is Harvey a failure of the assumption that we’ll adapt to climate change?
Harvey’s effects on petroleum pricing and related things
UPDATE:
I’m writing up Harvey here on its own post. This is going to prove to be an important hurricane. If you are in Texas get caught up right now.
UPDATE:
Well, finally, something interesting happened in the Atlantic! Tropical Depression Harvey is heading for Texas and in a very short amount of time is going to whip up into a hurricane and hit the Lone Star State right on the coastline.
From the NWS HPC:
1. Harvey is likely to bring multiple hazards, including heavy
rainfall, storm surge, and possible hurricane conditions to portions
of the Texas coast beginning on Friday.2. Heavy rainfall is likely to spread across portions of eastern
Texas, Louisiana, and the lower Mississippi Valley from Friday
through early next week and could cause life-threatening flooding.
Please refer to products from your local National Weather Service
office and the NOAA Weather Prediction Center for more information
on the flooding hazard.3. A Storm Surge Watch is in effect from Port Mansfield to High
Island, Texas, indicating the possibility of life-threatening
inundation from rising water moving inland from the coast during the
next 48 hours. For a depiction of areas at risk, see the Storm
Surge Watch/Warning Graphic at hurricanes.gov.4. The Potential Storm Surge Flooding Map is available on the NHC
website. This product depicts a reasonable worst-case scenario –
the amount of inundation that has a 10 percent chance of being
exceeded at each individual location. Because the Flooding Map is
based on inputs that extend out only to about 72 hours, it best
represents the flooding potential in those locations within the
watch area.
We still hear the yammering that climate change has not affected storms. “They said there would be more storms. There’s no more storms,” they say.
They are wrong in so many ways. For example, the total energy observed in tropical storms around the globe is up. There have been several big huge scary storms in the tropics in recent years, some of which are unprecedented in their size, strength, rapidity of forming, when they formed, where they went, and what they messed up. Other types of storms show either likely increases or, if not clearly increased yet, still show strong liklihood of increasing in the future based on models. Models that are good.
This is from Emannuel 2005, showing his “Power Dissipation Index” over time and sea surface temperatures.
This shows the long term up and down swings in total tropical storm activity, and an overall upward trend exactly as expected with effects from global warming.
This is from “Increasing destructiveness of tropical cyclones over the past 30 years” by Kerry Emanuel, Nature 436:686-688.
See also this post for more details.
Roger Pielke Jr. is one of those yammering fools (I used to try to be nice to him until he accused me of horrible things a few months back and almost none of them were true!) who will tell you this. Roger says, there have bee no more landfalling Atlantic Hurricanes in the US recently than ever before. But trying to figure out what is occurring on the Earth by only considering what the smallest of the Hurricane basins produces, and only counting the small subset of those hurricanes that hit the US (and, by thew way, ignoring some of them such as Hurricane Sandy in order to fudge the numbers) is like trying to get a handle on the frequency of major train derailments by watching the 100 mile length of track you drive along five times a year on the way up north fishing. Nobody would do that. Except Roger.
The normal number of named Atlantic storms is 12.1 of which 6.4 are hurricanes, and 2.7 major hurricanes, in a given year. The record high is 28 named storms, and the record low, is 4.
There have been various predictions for how much storm activity we expect this year. The predictions that are most recent and most reliable call for 11, 12, 11-15, 14, 11-17, and 15.3 storms. So, generally, close to average plus.
The prediction I watch most closely is from PSU’s Earth System Science Center. PSU has been making very accurate predictions for a number of years. For this year, they predict 15.3 +/- 3.9 named storms this year (i.e., about 11 to 20 with the best guess being 15). Their prediction will drop a little if there is a mild El Niño this year, but that seems increasingly unlikely. Also, PSU has a second alternative model that produces a lower estimate, of around 12.4.
So, in short, barring an El Niño, we can expect a near average but slightly above average year for Atlantic hurricanes. And no, that does not mean that global warming is not happening. It means that no derailments are expected along a particular section of recently maintained rail track.
Anyway, for the second year in a row, IIRC, we got cheated on our A storm. Below, I’ve put the official list of storm names for the Atlantic 2017 season (as headings, we’ll fill in info as the year progresses), but the first tropical storm to talk about today, 19 days into the season, is Bret (one ‘t’). Arlene happened last April.
Tropical storms don’t happen in the Atlantic in April. ‘Cept for Arlene. Generally, it seems like the boundaries are becoming enfuzzied. Expect more “extraseasonal” storms over the next few years, and expect eventually, perhaps a decade from now, for the National Hurricane Center crew to be asked to start watching year round, because a tropical storm that hits your fleet in April is still a tropical storm. Even if Roger says it doesn’t exit.
Bret
Bret formed near the very southern edge of the Atlantic Hurricane basin. 
This is the earliest far south forming hurricane in the Atlantic Basin. So, our first storm of the season happened months early, the second storm hundreds of miles south, compared to normal. Roger that.
Bret will menace the northern edge of South America, then in a few days from now it will be gone. Bret is not expected to strengthen and will not be a hurricane. Nor will it hit the United States of America. Therefore, according to Roger, Bret, as novel as it is, does not exist.
Cindy
The next storm, to be named Cindy, is very likely to form from a disturbance now seen in the south-central Gulf of Mexico. This is fairly typical place to see a tropical storm or hurricane form this time of year. Cindy will likely become a north-moving tropical storm, and will likely stay just at tropical storm strength, coming ashore somewhere between Houston, Texas and Morgan City, Louisiana. The chances of Cindy wetting down NOLA is very good, but again, this will not be a hurricane. This will happen some time late Wednesday, most likely.
While possible-Cindy would transform from a tropical storm to a depression with landfall, the storm will track up the Mississippi and cause lots of rain.