Bermuda, Leeward Islands, Mexico, and Japan … (TC’s for Thu 19 Sept)

Lots going on with two landfalls. Humberto is now moving away from Bermuda, after knocking power out, high waves and surge right on the coast, but damage seems light so far.   Lorena is brushing the west coast of Mexico, mostly a rain and coastal wave thing, and will hit Baja.  Damage should not be catastrophic (of course, if it’s your house, it’s a different story, but here we look at the big picture).  In things to come, the Leeward Islands of the Caribbean (Barbuda, Anguilla, St. Maarten/St. Martin, St. Barthelemy, Saba and St. Eustatius) have tropical storm watches in place since Jerry, as a hurricane, should pass close enough to cause tropical storm force winds and surf.  In the West Pacific, Tropical Depression 18 should become a tropical storm today before moving rapidly north and impacting Japan.    Otherwise, the main area of concern is the human-caused storm building on the Arabian Peninsula … and of course please don’t forget the ongoing recovery efforts in The Bahamas.

Here’s the maps:

Humberto, Imelda, and Jerry: Wed. Morning 18 Sept 2019

Humberto is on the way to brush Bermuda today, Imelda’s remnants are dumping rain on Texas, and Jerry is mid-Atlantic, might brush the Leeward Islands on its way to where ever it ends up, which at the moment doesn’t look like the US or Bahamas.  Monitor the National Hurricane Center’s “Key Messages” for the latest … the Near East Asia (Middle East) mess is distracting me right now so updates might less frequent than usual unless there is a serious threat.  Which, aside from flash flooding in Texas, there isn’t right now …

Tropical Cyclone Watch, Tuesday 17 Sep 2019

Although there are only two active storms this morning, one in the Atlantic and one in the East Pacific, there are a lot of disturbances with the potential to spin up in the next day or so. In the Atlantic, Humberto is generating some wave at rip currents along the US Southeastern coast, and may impact Bermuda later this week.  The rest of the Northeast US and Canadian Maritime Provinces will see waves from Humberto this week as well.

The disturbance about halfway between Africa and the Windward Islands is on the verge of becoming a tropical depression.  There is a system lingering on the Texas coast but the NHC only gives it a 30% chance of becoming tropical enough to call it a depression before it moves inland.

Hurricane Kiko is in that vast expanse of ocean between Mexico and Hawai’i, but not expected to make it to the Islands.  There are a couple of disturbances off of Mexico and Central America that the NHC is probably going to start advisories on later today or tomorrow.  And south of Hawi’i there are three weak disturbances, but none have much of a chance to spin up.

In the West Pacific, Piepah dissipated south of Japan, although another storm may spin up east of the Philippines that may impact Japan in a couple of days.

Bottom line: unless you are in Bermuda, or the west coast of Mexico/El Salvador/Guatemala, nothing to worry about at the moment.

Tropical Update, including Tropical Storm #Humberto

Although it disrupted relief operations, fortunately t looks like the worst stayed away from the Dorian ravaged areas.  The storm turning out to sea, towards Bermuda, which may have to deal with a hurricane Wednesday night into Thursday on the present track.  Here’s the forecast impact swath …

Elsewhere, there is a weak storm off of Japan, a stronger storm in off of Mexico moving away from land (Hurricane Kiko), and some waves in the Atlantic, only one of which has significant potential to spin up later in the week (60% chance per NHC).  There is a blob in the Gulf of Mexico that will bring rain to the Texas coast, but not likely to evolve beyond blobdom (that’s a technical term).

Tropical Storm Humberto (AL092019) Sat. Morning 14 Sept 2019

Overnight AL09 finally gained a closed circulation and 34 knot winds (40mph), the minimum required to get a name.  It is currently moving to the northwest, skirting the northern Bahamas; hopefully the worst of the storm will stay to the northeast, but unfortunately they will get some wind and rain, disrupting recovery efforts. As our attention here shifts to things besides hurricanes, please don’t forget about them; it will take years of efforts to rebuild and recover.

Humberto should encounter steering to the northeast, and a more favorable environment, so by Monday Humberto may well be a hurricane – but by then it will be turning away from the US.  The tropical storm watch for the Florida coast has been dropped, so they may feel free to resume their normal, no doubt legitimate, activities.  For the bucolic residents of the southeastern United States, even rain from the system is looking less and less likely.  By late next week the storm may be a problem for Bermuda.

Here’s the impact map based on this morning’s NHC forecast …

Elsewhere there are four areas on NHC’s tropical wave/area list, but none is really that interesting yet.  Tropical Storm Kiko is likely to become a hurricane before fading in the unfavorable waters of the middle eastern Pacific, well before it reaches the islands of Hawai’i.  Couple of invest areas in the West Pacific, one south of Japan might spin up today.

Decoding the NHC Forecast Advisory (AL092019 Update)

TL;DR: storm is still disorganized, tracks are trending to keep the storm offshore, and NHC may shift their forecast even further east later today.  Bahamas still needs to prepare, given the pre-existing damage.  The US Coast can just watch right now, but AL09 will likely become Tropical Storm Humberto later today.  Dangerous conditions are unlikely in the US, but worth paying attention in case that changes.  But read the rest; it’s Friday, not like you guys are working anyway 🙂

The National Hurricane Center produces two primary products: the Forecast Advisory, and the Watches and Warnings contained within it and the Public Advisory, that are based on the Forecast Advisory.  The other products are derived from these two primary products.  While the PA and FA are pretty clear, it takes some time and digging to interpret what they mean.  This is why I suggest your first step is the “Key Messages” product, which is a nice summary of the big picture.

The Forecast Advisory is at the heart of what NHC does.  It is a forecast for the storm position, intensity, and wind radii for the storm at fixed times in the future, out to five days, and is based on a careful study of the forecast models blended with forecaster experience.  The first 3 days are considered a forecast, the last 2 only an outlook.  That is because of the uncertainty that, while much better than it was even 10 years ago, is still significant.  As a text product it takes some decoding.  One of my key gripes with TV weathercasters is they normally focus on peak winds, and the maximum radius of tropical storm force winds.  The problem is that peak winds generally exist in a very small area of the storm – the intense damage swath of a hurricane is typically less than 30 miles either side of the track, and any significant impacts at all only 100 miles..  And these distances vary tremendously across a storm.  So you will hear things like “tropical storm force winds extend 200 miles from the center!”  That may be true in the NorthEast quadrant (which is generally, but not always, the strongest part of the storm), but elsewhere these distances can be half that far. The FA includes the wind radii in each quadrant.  Let’s take a look at the 5am FA for AL09 using the AWIPS II software used by the National Weather Service, with the forecast wind radii depicted … click to embiggen.  Note that the final two positions (96 and 120 hour, or 4-5 days from now) position generally doesn’t have wind radii estimated.

The blue arcs show the radius of tropical storm force winds (40mph).  Off of Jacksonville, the yellow arc shows 50 knot (56mph, the wind speed that things really start to break).  But there’s more: these are winds over water!  Over land they are typically 20% less due to friction.  So along the Florida coast, while those blue arcs go inland a bit, it is unlikely any areas other than within a couple miles of the beach will actually see winds that high, if the storm follows that exact track and intensity.  Now lets look at the latest advisory:

Not even any blue arcs on land.  That’s the raw data.  What I do is take that raw data and process it through sophisticated damage models.  Here’s the latest impact estimate from my new Stribog model, using this latest (11am Friday 13 September) National Hurricane Center forecast track and intensity.  What Stribog does is take the raw data from the Forecast Advisory (or any other track/intensity model, but I generally don’t show those in public to avoid diluting the NHC message), and using a coupled wind, wave, and storm surge model, it calculates the conditions along the track on a 982 meter grid.  Notice how asymmetric the damage swath is around the track. I then classify that (well, the computers do) in to easy to understand categories and display it using Google Earth to make a pretty map …

Potential TC #9 (AL092019); Finding the center?

Potential Tropical Cyclone #9 does not have a well defined center, and is still technically a tropical wave (if any terminology like potential tropical cyclone, tropical wave, etc. is confusing look here).   In the post-Sandy revisions to NWS procedures, if was decided that if it was possible the storm could reach watch or warning criteria, NHC would start advisories under the term “Potential Tropical Cyclone.”  It’s not done that often, only when a storm “spins up” close to land, like this thing is doing.  So where is AL09, where is it going, and how strong will it be when it gets there?  Let’s take a look at how NHC and TC specialists try to figure that out ..

First, where is the storm?  With weaker storms this is a big deal – the track models can’t do a good forecast without a closed circulation to lock on to.  Here are all of the position fixes for AL09, and the “track” NHC is using … as always, click to see full size.

Compare that with Hurricane Dorian as it traversed The Bahamas as a much stronger and well defined storm … the icons are for various techniques like satellite position/intensity estimates, airplane fixes, radar, etc.

Here’s the tropical analysis for this morning, with the IR satellite view (sun isn’t up yet!).  The big bad orange blob, the main rain and convection associated with the system, is to the right of the “L” marking the estimated center (the Low pressure marker).

The lack of a solid circulation to lock on means you have to treat the track models a bit skeptically.  Here’s the full spread for AL09, including ensemble members.  A big confusing mess …

The red line is the official NHC track.  They are essentially splitting the difference between the various scenarios given by the “deterministic” model families (colored lines).  Intensity is an even harder thing to figure out.  Conditions are not favorable for the storm to develop over the next two days.  After that, conditions should improve, but by then the storm may be near or over Florida, limiting development.  So without a good track, doing an intensity estimate is a harder than normal task (and intensity is a harder problem than track in most storms).  NHC is conservatively assuming the storm will stay on or near shore, but still be able to take advantage of the favorable upper level winds to strengthen into a moderate tropical storm.

So what does all that mean?  Well, for people who want to fill the airwaves or bandwidth with confusing speculation, it’s a windfall (see what I did there 😛 ).  But for you, the sophisticated reader, you do what you always do since you have a plan, restocked your supplies after Dorian (including, if comments on Facebook are any guide, your extensive wine cellar), and look at the NHC Key Messages product, and check for watches and warnings. Here’s the estimated impact based on the NHC forecast …

Bottom line: much weaker storm than Dorian, might follow a similar track (or not), not likely to become a hurricane in the near term, mostly a rain and blustery wind thing.  More misery for The Bahamas.  Inconvenience in the US, with the potential for hazardous, but not likely dangerous conditions right on the coast.

Invest in The Bahamas now a “potential tropical cyclone nine” (AL092019)

NHC relocated the center earlier today, causing the tracks to jump around and giving the chattering class something to talk about, and as of 5pm has started official advisories and tracking. Remember that for weaker systems, often there isn’t a real “center of circulation” that the track models can latch on to.  Whenever there is a relocation (in this case over 90 miles), the models will often jump – best to wait for a cycle or two for them to settle down before getting excited (see a pattern here?).  Again, with hurricane/tropical cyclone tracking, watch the trends!  Here’s the official forecast track and impact estimate …

Note that the GFS takes the storm across Florida and into the Gulf.  That is still a very real possibility, given the yuge uncertainty in the tracks.  Either way it will spread more misery in The Bahamas, and cause wind and rain in Florida in areas still heavily drinking from the near-miss from Dorian.  Those in Florida should probably check in on the 11pm advisory and monitor what your local EMA’s are saying; those further north can wait until in the morning to panic.

Storm this weekend? (Thu, 12 Sept 2019)

The system being monitored as AL952019 is moving through The Bahamas today.  NHC gives it a high (80%) chance of development over the next few days. Here’s the available track primary track models early this morning.

The models mostly keep the storm below hurricane strength, and many don’t even bring it up to tropical storm intensity.  In any event will bring rain and perhaps some gusty winds to South and possibly Central Florida. I suspect it’s not helping the Dorian recovery efforts.  If it goes in the Gulf of Mexico (GOMEX), it might have a chance to spin up a some and threaten the eastern Gulf Coast*.  But that’s a next week thing, and not time to worry about that right now.  

So what’s the bottom line – when should you follow, and worry about, an “invest area”?  Short answer is you shouldn’t.  If it were an actual threat, NHC would start tracking it as a “subtropical system” and begin issuing advisories.  Note that as of 8am, NHC says they might start issuing advisories later today if development continues.  That’s when you should start paying attention.

* I’d say it could potentially impact East Mississippi, a dig at CNN, who mislabeled Alabama as Mississippi in some of their Dorian graphics, or Sharpieland, in reference for the US President’s art work which is major threat to national security or another example of fake media depending on your perspective, but folks don’t seem to have much of a sense of humor about this stuff any more.

System in The Bahamas

Statistically, if you are hit by a tropical system, there is a about  a one in four chance you will be hit by at least one other tropical system of some kind in the same year.  If you think about that it makes sense, since the “steering currents” and formation zones tend to follow larger climatalogical patterns.  Unfortunately, it also increases the misery of those impacted by a major storm and those trying to help them, even if they don’t become named storms.  We’re seeing this with The Bahamas (BTW, for those grammar nazi wannabes who asked 😛 , yes, the “T” is supposed to be capitalized when referring to the country since it’s a proper part of the name).  There is a disorganized system approaching from the east, being tracked as AL952019, with clouds and showers starting to spread over the islands …

NHC gives this thing a 40% chance of spinning up in the next two days, and a 60% by the time it reaches the Gulf of Mexico.  The track models currently have it as a weak system approaching the coast of, um, one of those states in the Eastern GOMEX between Florida and Louisiana.  Not saying the name.  Too politically sensitive right now …