Visible GOES-17 satellite image of Potential Tropical Cyclone Nine at 15:20Z (11:20 a.m. EDT) Wednesday, July 29, 2020. (Image credit: NOAA/RAMMB)

A large and vigorous tropical wave in the eastern Caribbean, designated Potential Tropical Cyclone Nine (PTC 9) by NOAA’s National Hurricane Center, was spreading heavy rain showers on Wednesday over much of the Leeward Islands, Virgin Islands, Puerto Rico, and the Dominican Republic, as seen on long-range radar out of Puerto Rico and Martinique.

Rainfall amounts in the islands as of 11 a.m. EDT Wednesday were mostly less than an inch, though a personal weather station on Dominica received 3.13″ in 24 hours.

As of that time, PTC 9 had top sustained winds near 45 mph and a central pressure of 1006 mb, and was headed west-northwest at 23 mph. PTC 9 is predicted to bring tropical storm conditions with heavy rains of 3 – 6 inches to the Leeward Islands, the Virgin Islands, Puerto Rico, Dominican Republic, northern Haiti, and Turks and Caicos Islands over the next few days. Higher rainfall amounts of 4 – 8 inches were predicted for the Inagua Islands.

Figure 1. A heavy rain shower from PTC 9 moving in over St. Barts in the Leeward Islands at 9:09 a.m. local time July 29, 2020. Thanks go to Caribboy for this link. (Image credit: webcam)

An Air Force hurricane hunter aircraft investigating the storm Wednesday morning was unable to find a well-defined surface circulation, so PTC 9 retained its ungainly moniker. Satellite images on Wednesday showed that PTC 9 was steadily growing more organized, with more low-level spiral bands and an area of intense thunderstorms consolidating near what appeared to be a developing surface circulation center. The storm is also expected to slow down in forward speed through Thursday, favoring development and making it likely that PTC 9 will be named “Isaias” (pronounced ees-ah-EE-ahs) by Wednesday night. If so, that would beat the record for earliest ninth storm in Atlantic tropical cyclone history set by Irene on August 7, 2005.

PTC 9 had favorable conditions for development on Wednesday afternoon, with sea surface temperatures (SSTs) near 29 degrees Celsius (84°F) and light wind shear of 5 – 10 knots. The system was embedded in a moderately dry atmosphere with a mid-level relative humidity of 55%, but the light wind shear to a large extent was allowing the storm to wall off the dry air of the Saharan Air Layer to its north.

Figure 2. Predicted surface wind (colors) and pressure (black lines) at 6Z (2 a.m. EDT) Friday, July 31, 2020, from the 6Z Wednesday, July 29, 2020 run of the HWRF model. The model predicted that PTC 9 would be approaching the Bahamas as a disorganized tropical storm with peak winds of 48 knots (55 mph, yellow colors) and a central pressure of 999 mb. (Image credit: Tropical Tidbits)

Forecast for PTC 9

The prospects that PTC 9 eventually will attain hurricane strength look dimmer than they did on Tuesday, but the uncertainty in the future of the storm remains very high until it forms a well-defined center and gets named.

As PTC 9 moves west-northwestward, it will have to contend with passage over Hispaniola on Thursday, and the mountainous terrain on the island could significantly disrupt PTC 9’s circulation. Passage close to the mountainous terrain of eastern Cuba on Friday may also act to disrupt the storm. In addition, PTC 9 will also have to contend with dry air from the Saharan Air Layer, located to the north. The 12Z Wednesday run of the SHIPS model predicted that the atmosphere surrounding PTC 9 would slowly dry to a relative humidity of 45% by Thursday evening. The model also predicted that wind shear would rise to a moderately high 15 – 25 knots on Thursday through Saturday, which should retard development.

However, SSTs for PTC 9 will warm to 30 degrees Celsius (86°F) by Saturday, which will aid the intensification process. Also favoring intensification will be a large-scale region of ascending air over the Atlantic, caused by passage of an atmospheric disturbance called a Convectively Coupled Kelvin Wave.

The 11 a.m. EDT Wednesday National Hurricane Center (NHC) intensity forecast called for PTC 9 to remain below hurricane strength, peaking with 60 mph winds this weekend. Nearly all of the top intensity models also predicted that PTC 9 would not become a hurricane.

The three best models for predicting tropical cyclone genesis – the European, GFS, and UKMET models – all support intensification of PTC 9 into a tropical storm by Thursday, July 30. In an 8 a.m. EDT Wednesday Tropical Weather Outlook, NHC gave PTC 9 two-day and five-day odds of formation of 90%.

PTC 9’s rains beneficial for drought-stricken Caribbean islands

Many of the Caribbean islands in the path of PTC 9 will welcome its heavy rains, since they will help alleviate moderate to severe drought conditions from an unusually dry spring and first half of summer.

Figure 3. Palmer Drought Severity Index (PDSI) for Puerto Rico and the U.S. Virgin Islands for July 23, 2020, showed much of the islands in moderate to severe drought. Regions marked with an “S” imply mostly short-term impacts to agriculture. (Image credit: U.S. Drought Monitor)

Climate change is likely partly to blame for the drought, as explained in a 2018 study, Exacerbation of the 2013–2016 Pan‐Caribbean Drought by Anthropogenic Warming. The authors of that research found that human‐caused warming contributed to 15 – 17% of the severity of the intense 2013 – 16 drought in the Caribbean, and 7% of its spatial extent. The findings “strongly suggest that climate model projected anthropogenic drying in the Caribbean is already underway, with major implications for the more than 43 million people currently living in this region,” they concluded.

This year’s drought is particularly acute in Puerto Rico, where over half of the island was in drought on July 23, according to the U.S. Drought Monitor product. The governor declared a state of emergency in late June and ordered water rationing, subjecting residents in affected areas to 24-hour water shutoffs every other day. Loss of running water makes living through a pandemic deadlier, since residents are unable to wash hands, bathe, and disinfect surfaces as often as needed to avoid spread of the coronavirus.

How inequality grows in the aftermath of hurricanes

According to Princeton’s Latin American Flood and Drought Monitor, the Dominican Republic is experiencing the worst drought in the Caribbean. To illustrate, rainfall amounts between June 15 and July 27 at Barahona, on the southwest coast of the Dominican Republic, were just 0.09″ (2.2 mm). The capital, Santo Domingo, received 0.44″ (11.3 mm) during the same period. Haiti is also under severe drought, putting much of the nation into a food crisis, according to the Famine Early Warning Systems Network.

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Jeff Masters

Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a...

365 replies on “Rain from Potential Tropical Cyclone Nine brings drought relief to Caribbean islands”

  1. Got it. Spotted Cow, Miller High Life, spiked seltzers and Michelob Ultra right here.

  2. Andre thank you for trying to turn a new leaf here. Don’t let those who target you with downvotes get you down. There are far far more rooting for you. Stay on topic and give us more deep insights to your thinking. Autism is not your crutch. It’s what makes you unique. Sure waiting and rooting for you to opine like I know you can. WU blog, thanks Jeff, now YCC, was always about helping those who needed it. Compassion at it’s heart. I hope YCC is too.

      1. Yeah, Andre, I hope you feel better. There’s a rainbow at the end of every storm, and I sincerely hope you get there.

      2. You know I am a fan. Keep posting your pics and putting in your comments. A lot of the time you draw our attention to entities we might otherwise miss. I’m holding both thumbs up here!

    1. A few days ago I am sure that one of the models had this as two storms. At the time I thought, that’s impossible, but now I wonder if that is what they were seeing.

      1. I had asked about this, if it was possible. I got only one very generalized response. I was genuinely curious. But this commenting system isn’t conducive to enhanced discussions. And comments get lost/shuffled quickly into near-oblivion. Oh well.

  3. Is there an app for that???

    Okay, so most may already know I geek out over clouds. But seriously. I need some advanced warning system. Like an app that notifies me: “Sunrise is going to be spectacular. In 9 hours. So, be awake, be prepared, go out to (exact coordinates) because you’ll have roll clouds, lenticular clouds, and gunpowder pink skies. Sight lines in your local area are obviously no bueno – power lines everywhere, ugly buildings, obstructed viewing, etc.”

    Is that too much to ask for? LOL.

    So, I did somethin’ a lil different. A cloud composite:

  4. ptc 9 seems to be really hauling tail, I probably don’t remember but I don’t think I have ever seen a system move that fast.

    1. I hope it keeps on keepin’ on. I mean, no better way to keep it from more fully organizing, right? This is expected to slow its rate. And from experience, I’d take a fast-moving low Cat 3 (which I highly doubt it would ever become) to a slow-almost-stalled giant low Cat 2 (still improbable IMO). Every time.

  5. The blog is split between the two sites at this moment… a fitting comparison to PTC 9 being split between N and S!

  6. Test, I don’t know if it is my iPad or what, but is easier to reply than post new for me.

  7. I want to “login” but how? I can’t find a way to “register” which usually one needs to do first. Long time follower of this blog, but never posted, mostly because I love weather but don’t know too much about it (and it’s so complicated it’s hard to learn, but I glean what I can).

    1. And appears to be consolidating. Finally. Still rolling on like a tire and not whizzing through like a frisbee. Which means no westerly wind component.

  8. Deep convection has continued to increase in association with the
    disturbance since the previous advisory. More recently, a band has
    developed over the southwestern portion of the broad circulation
    and it appears that the system may be closer to acquiring a
    well-defined center. Earlier ASCAT data that arrived shortly after
    the release of the previous advisory revealed a large area of 35-40
    kt winds well to the north of the vorticity maximum. This
    supports maintaining the initial intensity of 40 kt.

  9. Just a question for site navigation? Is it possible to put the page navigation at the top of the comment list as well as the bottom? As it is you need to scroll to the bottom to see whether you are on the most current page, if you have been away for awhile and refresh. Thanks for all the work that has been done to get the comments onto the blog. Very impressive.

    1. We’ll see. Remember not to hang your hat on a single system— this thing seems fickle.

      How are you today?

      1. Hey, please feel better. Whether this storm develops or not, the Atlantic has plenty of stuff ahead. Plenty! And you’re gonna be there to track it and tell us all about it. I’m sorry you’re not feeling great, Andre, so feel better my friend!

    2. I guess that means PTC 9 is a bust? Or should we wait for more developments?

      nah I already know to wait and see what happens

  10. I doubt that this storm will ever make a serious run at hurricane strength for 3 reasons:

    1. It is so messy at this point it’s not even funny. Fast movement and large size means that it will take a lot of time to organize before it can start ramping up. But it’s not going to have that time because…
    2. It’s going to hit Hispaniola. That will make it even more disorganized if not kill it, as it won’t have enough time to form much of an inner core before it makes landfall.
    3. Conditions after Hispaniola are less favorable, with lots of dry air and later on higher shear as well. A strong hurricane might be able to hold these off and take advantage of the warm waters, but this storm will be hard-pressed to do anything at all.

    I’m normally quite a wishcaster but everything about this storm tells me that it will be a major underperformer.

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