NHC Starts tracking on Potential Tropical Cyclone Five forms, headed to Caribbean

The US National Hurricane Center started advisories on PTC Five at 5pm this afternoon. Here is the forecast impact swath …

TAOS/TC Impact swath based on 5pm NHC Forecast; click to you-know-what

The main reason to get this started is, like Danny last weekend, there isn’t a lot of time to get watches and warnings in place, and in this case there is a good chance it will become a tropical storm, so this starts the administrative ball rolling. Tropical storm watches are not up for the windward islands. It’s moving very fast, which should keep it from getting much above a middle grade tropical storm (50 knots). The other big issue is things are very uncertain beyond 72 hours so NHC just held the intensity and track more or less constant after that. Expect changes over the next day or so as the storm consolidates (rather, if and how it does so), and the models get a better lock on things.

The storm isn’t a threat to the US at the moment – but obviously is pointed in the wrong direction. If you live in the Southeast or Florida, and your hurricane plan is solid, no need to do anything. If it isn’t, take a look at the FEMA/DHS web site for advice.

As always your best summary of warnings and the NHC forecast are the Key Messages regarding Potential Tropical Cyclone Five (en Español: Mensajes Claves).

Watching the Atlantic: when to start paying attention

The US National Hurricane Center has given one the two “invest” areas in the Atlantic a 70% chance of becoming a tropical cyclone in the next five days, and the graphic that accompanies the Tropical Weather Outlook (TWO) product is in ominous red. The usual suspects are starting to get excited. Should you worry?

The key thing to look at in the TWO product is in the text. Here is what NHC has to say about the more eastward system (with the temporary ATCF ID AL972021, aka 97L):

A broad area of low pressure, associated with a tropical wave, is located about midway between the west coast of Africa and the Windward Islands. This system is producing a large area of showers and thunderstorms that continues to show some signs of organization.
Environmental conditions appear generally favorable for development, and a tropical depression is likely to form during the next few days while the system moves west-northwestward at about 20 mph. Interests in the Windward and Leeward Islands should closely monitor this system as it will likely be moving through that region on Friday.
Formation chance through 48 hours…medium…50 percent.
Formation chance through 5 days…high…70 percent.

NHC TWO as of 2am ET, Wed. 30 June (bold added): https://www.nhc.noaa.gov/gtwo.php?basin=atlc&fdays=5

The key phrase is in bold. As noted in other posts, NHC will use the magic words “interests in <someplace> should <do something>” when it’s time to start paying attention. In this case, those in the Caribbean should start paying attention. “Monitor” tells you to review your hurricane plans, check your supplies, and look at the NHC site periodically to see if things have changed, but it’s not yet a serious specific threat.

What about the US? Way too early to say. The current track model map might cause some excitement and angst in Florida and the Southeast …

But run-to-run consistency hasn’t been good beyond about 4 days. Yesterday the forecast for next week (Wednesday 8 July) had the system jumping from Louisiana to Georgia. There are always two questions about tropical systems: where and how bad. At this point, where is the Caribbean in the next 3-5 days. How bad is “maybe a tropical depression but we don’t really know yet if it will get stronger than that.” If your question is “what about next week” the answer is “somewhere from Mexico to the middle of the ocean as anything from clouds to a hurricane.” So, like every day ending in a “Y” between June and November, have a hurricane plan, get on with your life, check back tomorrow and see if anything develops …

An important footnote:
Social Media can be a terrible way to get storm information if you aren’t careful. These situations can change pretty rapidly, last weekend’s Tropical Storm Danny being a great example. Some platforms like Facebook by default show you items ranked by popularity rather than chronologically, so be sure to check the posted time to make sure you are seeing the latest.

Tropical Storm #Danny wrapup; invest in the Atlantic; Enrique near Mexico

Danny has dissipated over central Georgia this morning (although some thunderstorms, displaced well west of the old center do persist) and NHC issued its last advisory at 5am Tuesday morning. Here is the final swath using my TAOS/TC model, based on the official NHC data:

Final impact swath for Danny; click to see full size

In browsing the Local Storm Reports this morning, nothing too serious stood out. Trees down, scattered street flooding and power outages, some heavy rain in a few places. The WSAV TV tower was hit by lightning twice. Sustained winds were fairly light inland, a few gusts in thunderstorms. If you weren’t told this was a tropical storm you’d probably think it was just a normal bad afternoon thunderstorm episode.

The invest area in the mid Atlantic that NHC is watching is still tagged with a five day probability of 40%. Once it gets further west and enters the Caribbean conditions are a bit more favorable for something; we’ll just have to wait and see. Remember that the majority of these things don’t ultimately spin up; don’t worry until you need to.

Enrique continues to parallel the western Mexican (Pacific side) coast, weakening as it approaches Baja. It should make landfall as a minimal tropical storm on the south tip of the peninsula tomorrow. Flash flooding and mudslides continue to be a problem across the mountains along the coast, even though the storm has yet to make landfall.

TD4 is now Tropical Storm Danny

Tropical Depression Four is now Tropical Storm Danny according to the National Hurricane Center, based on aircraft reports, radar, and convection (thunderstorms) are starting to converge around the center as seen on satellite. Here’s the satellite view …

GOES East Visible just after 2pm, L marks the center

and here’s the radar from shortly after 3pm ET, you can clearly see a spiral pattern coming into range (and being):

Hampton (CLX) radar, reflectivity on the left, velocity on the right – click to embiggen

Nothing has changed since the last time nothing changed as far as the impacts go, except as noted now insurance deductibles are probably a lot higher if you are unlucky and get some damage (which should be fairly rare and limited). There is a small chance for a weak waterspout or tornado – WFO CHS just pushed an offshore warning on that for offshore, especially Hilton Head and points north – so keep your weather radio on, especially in the Charleston area. Savannah may still get a thunderstorm out of this but we’re on the back side now; the real action (such as it is) will probably be north of HHI/Beaufort.

NHC Starts tracking on Tropical Depression Four (AL042021)

NHC has started tracking on Tropical Depression Four (AL042021), and a Tropical Storm warning is now posted for part of the South Carolina Coast from Edisto Beach to South Santee River. Here’s the impact swath from my TAOS20 model, using Forecast Advisory #1 (11am, Monday 28 June 2021).

TD4 “Damage” Swath Forecast, click to enjoy full size.

The bottom line hasn’t changed since this morning, even if some tropical storm force winds are detected offshore and Danny forms, the pipes will soon play and it will deteriorate quickly. The physical effects are going to be about the same either way: rainy afternoon and overnight, landfall this evening, although now the worst of it is forecast to be towards the Charleston area rather than Savannah/Beaufort. Maybe some localized street flooding with over an inch of rain, winds don’t look bad at all right now, and you might see some gusts and branches down, that sort of thing. Savannah will probably be just some rain.

Well, there is one potential major impact: if NHC does declare this to be a tropical storm before landfall, in the unlucky event you do get damage from this thing, your deductibles just jumped from standard to “named storm”. Be sure to thank your insurance commissioner next election …

Hires color image of system approaching Georgia coast

Click to embiggen this GOES East rapid scan view of, um, whatever it is.

Here is the view from the one minute “mesoscale sector” GOES scans at 10:07am … this is a really interesting image since you can very clearly see the low level circulation center (the swirl on the right) is separate from the thunderstorms and “worst” of the weather. In simplified terms, this is why NHC hasn’t started advisories, warnings, etc. on this storm: it isn’t really a tropical cyclone yet (if it will ever be). The concern is that when that circulation crosses the Gulf Stream it will develop thunderstorms around the center and thus qualify as a TC.

In practical damage terms, as noted before, if this thing does become a depression before landfall or not won’t make too much difference. However, if it does become a “named” storm, it can make a lot of difference to your pocketbook if you are unlucky enough to get any damage since it will change your deductible. Not fair, but that’s the system your insurance commissioners have set up …

System approaching #Georgia Coast today

TLDR: it doesn’t really matter much if the NHC starts advisories or raises warnings in terms of impacts, the physical effects are going to be about the same: rainy afternoon and overnight, “landfall” this evening. Maybe some localized street flooding with over an inch of rain, winds don’t look bad at all right now, maybe a bit higher in South Carolina, and you might see some gusts and branches down, that sort of thing.

Here’s the details … The system moving towards the Georgia coast hasn’t organized much overnight, so the National Hurricane Center hasn’t started official advisories or raised any warnings as of 6am. Here is what it looks like on satellite (water vapor band, with surface analysis map overlay so you can see where the “center” is located – the L symbol):

Water Vapor Band and surface analysis, 6am Monday

The Charleston radar (which is really in Hampton, SC, about half way between Charleston and Savannah) is showing the outer rain blobs (not really bands at this point if ever) approaching the coast:

Radar from “Charleston”: reflectivity on the left, velocity (wind speed) on the right,

At the moment the impacts of this thing don’t look so bad. Could get some heavy rain, totals of an inch or more in the Savannah/Hilton Head/Beaufort area. It’s moving fairly fast so while there is some potential for minor flooding, flash flooding isn’t too likely. Winds look well below tropical storm strength; if it does organize enough to reach depression criteria, the winds should stay confined to the coast (the islands) but even then not really a big threat. On the beaches there is a rip tide caution, and any time these things come ashore there is a chance of waterspouts or weak tornadoes (EF0/1). So keep your weather radio on just in case. Serious rain should kick in around noon, and be gone by tomorrow morning.

AL962021 (Invest off of Georgia Coast)

Well, that changed quickly. The open trough south of Bermuda, north of Haiti, and of course east of Georgia (the hot and sticky one) has gotten a lot more organized over the last few hours, and NHC is a bit more enthusiastic than they were this morning and now give it a 50% chance of becoming a system. Here’s the latest IR (left) and visual (right) view from GOES East – the system is the blob due east of the GA coast:

Satellite view of AL96 (click to embiggen)

The main concern is that overnight and tomorrow it will be crossing the Gulf Stream, with a lot of deep warm water, and it could rapidly intensify/organize into a real tropical system. Here are the track we have at the moment … not a wide selection yet, and the GFS Global Model (blue line) weakens even the initial intensity so it doesn’t get any stronger than it is now, but at this stage of development none of the models are what we would call reliable, and it wasn’t initialized with the current state of organization.

Track models as of 2pm ET Sunday

The forecast model tracks mostly have it headed into the upper GA or South Carolina coast, at worst as a weak tropical storm, with conditions deteriorating tomorrow and landfall overnight Monday/Tuesday. The Tropical Weather Outlook doesn’t have the magic words in it; at this point still not likely to be a serious threat even if it does spin up some, but worth keeping an eye on.

Atlantic Invests; #Enrique brushes #Mexico

It’s that time of year when the US infotainment system (aka news) does its thing with respect to hurricane season, and we’re off to a great start with headlines like “Two storm systems being watched in Atlantic, neither showing signs of threat to US yet” (Florida Sun-Sentinel). Well, to start with, they aren’t storms. They are “investigation areas.” Here’s a link to a discussion on “Invests” on NHC’s blog, but the important thing to keep in mind is this:

It’s important to recognize that the designation of a disturbance as an invest does not correspond to any particular likelihood of development of that system into a tropical cyclone. Indeed, we will open an invest in part to help us determine what that likelihood is. Also, and particularly near the beginning of the season, it’s not uncommon for NHC to create one or more invests solely to test data flow or model processing scripts. The Tropical Weather Outlook should always be consulted to determine the significance or potential threat of an invest disturbance.

From NHC Blog, https://noaanhc.wordpress.com/2014/07/31/investing-for-meteorologists/

This morning (Sunday 27 June 2021) we have two areas noted on the hurricane center’s “Tropical Weather Outlook” or TWO, one of which has active model tracking under the temporary ATCFID AL952021. The other may get the designation AL96 when model tracking starts. But here is the TLDR: neither has much chance of development at the moment. The one between Bermuda and the US, with the “cone of shame” pointed at the Georgia coast, has a 20% chance of developing into a tropical system. The one further out is tagged with a 30% chance of development in the next five days.

When reading the TWO the phrase you want to look out for is “interests in <some place> should <do something>.” Unless you are in the areas mentioned as “<some place>,” you really don’t need to worry much about the system; if you are <some place>, then <do something>. Very simple! If, as is in this case, the magic words aren’t there, it’s nothing to worry about. Especially when a potential development area is close to the US, the hurricane center is pretty conservative and will say something if there is any chance of the system becoming a problem.

Here is the current (as of 7am) satellite image with the TAFB Surface Analysis. For a primer on how to read the symbols on these maps look at this link. You can see the low pressure symbol (“L”) that marks the location of invest area AL95 at the lower right, off of Africa, as well as the line of tropical waves (TRPCL WAVE) marching across the Atlantic. And off of the US, above Haiti in the center of the map, you can see the dashed line marking a trough, that is the area that NHC has marked at 20% pointed at the US, but does not yet have model tracking because it has no real center to lock on to.

Current Atlantic Surface Analysis from TAFB (Sunday Morning 27 June)

Also of interest on the right is a large fuzzy area seen in the satellite image – that’s dust and sand off of Africa that is inhibiting storm formation in the Eastern Atlantic.

In the middle left side, off of Mexico, is the hurricane symbol marking the position of Hurricane Enrique (still in shadow this early in the morning). A reminder, whenever there is an active storm that threatens land NHC produces a great summary product called the “Key Messages.” Here’s the one for Enrique. It’s a nice rollup of the important things to know about a storm in relatively drama free format. It should be your first go-to product when deciding if you need to panic or not. Speaking of Enrique, it is paralleling the west coast of Mexico and looks to make landfall on Baja as a deteriorating tropical system in about four days. As noted in the key messages, the big threats here are heavy rain, flash flooding, and mudslides.

Hurricane Enrique (Sat 26 June)

While the Atlantic is quiet (the invest AL95 off of Africa now has only a 10% formation chance), Enrique has strengthened into a hurricane this morning as it parallels the west coast of Mexico. Here’s the latest forecast impact swath:

click to embiggen.

Enrique is in a favorable environment right now and should continue to intensify. While there are tropical storm warnings for the coast near and south of Puerto Vallarta, the biggest risk at the moment is from flooding and mudslides in the coastal mountain ranges … some areas could see 8 to 10 inches of rain over the next five days.

GFS five day rain accumulation