Are there really three Atlantic storms?

Technically yes, but it’s complicated if you are trying to compare this year with history. First let’s review what we have, then consider what (if anything) it means. Still watching the decaying remains of Hilary, now over Nevada. Radar this morning shows it is still raining across the LA basin and other parts of the region …

so WPC’s advice this morning still holds: Hilary is expected to produce a potentially historic amount of rainfall that may cause life-threatening to locally catastrophic flash, urban, and arroyo flooding including landslides, mudslides, and debris flows through early Monday morning. Here is a link to NHC’s Key Messages regarding Post-Tropical Cyclone Hilary (en Español: Mensajes Claves).

Last night the US National Hurricane Center started advisories on two additional tropical storms, so we now have Emily, Franklin, and Gert …

Of these, Emily and Gert are both falling apart and no threat to land. Franklin is forecast to cross the Dominican Republic, bringing rain and gusty winds to both Hispaniola (Dominican Republic/Haiti) and Puerto Rico. Given the mountainous terrain of both islands, this means a risk of flash flooding and mudslides through the middle of this week. On this track it will bring tropical storm conditions to upwards of 9 million people, with economic impacts between $80 and $100 million USD. After crossing the Greater Antillies, Franklin is forecast to become a hurricane late in the week, but by that time should be headed northeast, away from land.

The other system to watch is invest AL91, currently west of Key West and entering the central Gulf of Mexico. GFS (shown in the map above) is showing it becoming a tropical storm just before landfall, and NHC has it tagged with a 70% chance of doing so. I wouldn’t be surprised if they start advisories on the system as a “subtropical storm” today, even if it hasn’t spun up yet, since there might not be much notice before landfall (which looks to be Wednesday). The official word, from the outlook:

A tropical depression or storm is likely to form while it
approaches the western Gulf of Mexico coastline by Tuesday.
Interests in the western Gulf of Mexico should monitor the progress of this system. Tropical storm watches or warnings may be necessary on Monday for portions of the southern Texas and northern Mexico coastlines.

So, what is going on? Is this really a potent of climate doom? First, to be clear, the earth’s atmosphere is in fact changing in anomalous ways, and it’s almost certainly due to human activity. However, when looking at tropical cyclone (hurricane) activity, it’s really hard to pin things on climate change just looking at the numbers. For one thing, short lived storms like Gert would not likely have been given names and numbers before 15 or 20 years ago, much less prior to the satellite era. It’s more than likely that, using the standards of even the 1970’s,1980’s, or 90’s, we would only be on storm number 3 or 4 in the Atlantic, not number 8. That’s not some conspiracy or deviousness on the part of meteorologists, that’s simply because we have better observing systems like microwave radar equipped satellites, high resolution imagery from the new GOES-R series, and so forth. So at the end of this year when the inevitable rash of popular stories appears about how busy the season was despite El Nino, be a bit skeptical – there is more going on than it might appear from just the raw numbers.

Another factor is that the purpose of the National Hurricane Center is to provide watches and warnings. Take AL91 – it might become a tropical depression or even tropical storm less than a day before landfall. In order to provide adequate warnings, they need to start the formal advisory process before it actually becomes a storm so that preparations, that take time, can take place. In addition, they need to prepare people for what might happen, not what is most likely to happen. So they need to assign a number, and maybe even declare it a tropical storm, when in fact it does not (and never will) meet the formal criteria as a tropical storm. That will be sorted out after the season, but by that time the “we had an above average season because the number of storms was X!” will already be ingrained in the public perception. So, this is all more complicated than it looks on the surface, and as I frequently rant, counting storms is not always a great metric for how bad a season is.