PTC 9 on July 29
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. Thanks, Skyepony. Huh wonder what’s wrong. I know sometimes link verifications get really finnicky about things like whether “www.” is included or the difference between “http:” and “https:” but thanks for your continued excellence and blog posts. Keep on keepin’ on! Persevere! ; )

      1. Thanks for the suggestion. Will have to check it out when I get a chance. May have put my link in wrong too. Also maybe something else lost when gained mod permissions.

  1. Put together a blog with some self updating graphics on Isaias & a photo gallery of him started. Starting to get ready for the storm here so didn’t get to writing many words yet. Looks like he’s jumping the gap.. If you click on my handle here it should take you there.

  2. It seems Isaias will provide fine rainfall for the islands and appears more and more likely not to impact mainland USA with a direct hit.

  3. I thought if I hit refresh, most recent comments would appear, but that didn’t happen. Any advice? TIA

    1. Hi. My experience is that once I stray to any other page than the landing page (i.e. I sort comments in any way or click “Page X” of comments), then I go back up to the URL address and remove everything after the last “/” of the article. Then press “enter” to refresh the page. Newest comments will appear.

      Current article, remove any text after “___to-caribbean-islands/

    2. Refresh works for me, unless the blog has moved on to a new page. Then I have to scroll to the bottom and click Next to advance.

  4. Keep, can you see why I’m getting a banned notice from WU 🙁 I’ve been there forever and don’t think I did anything wrong…. thanks 🙁

      1. You don’t look banned there at all. This is where the community is moving to so maybe just settle in here. Welcome back!

      2. So strange! I’ll check again since I’m back on WiFi! Yeah, I’m ready for the move, but am not a big fan of change, after over 10 years (mostly lurking) on the other site, it’s “home” lol. Thank you and thanks for the new blog post! Keep up the good work!

    1. Sometime in the relatively near future that country and some of the surrounded territories will become uninhabitable. I’ve felt for some time that is a motivating factor to some degree for the aggressive actions of some of those nations…they will need a new home, and they’re ‘scouting’ for it now. Oceans rising and drought claiming more territory is a political dynamic. That should not faze us here; we’re just witnesses to disruptive weather, the real long term power of this planet.

  5. Sure be nice if they shut down comments on the old site so we could get everyone over here!

    1. I’m not sure that you would want that to happen yet.

      A trickle of people using the site will give them a chance to adjust as they go and let the mods catch up on the new comment engine. I don’t think that I could stand the whining that would happen if everyone showed up at once (especially Grothar! 😂 ❤️ )

      1. I think that Gro is focussed on healing at the moment. When he feels better, I am sure that he will show up. That will be a good day and there shall be celebration throughout the land! 😁🎉

    1. our climate is accumulating 4 Hiroshima atomic bombs worth of heat every second. That´s a lot of energy every second to be honest hard to believe.

      1. I know, right?! Just insane. Thanks for checking it and posting that summation (that I didn’t).

  6. Yes! So happy to be away from the Weather Channel and to find the 2 best Tropical Bloggers back in business!

  7. Apologies in advance, there are no instructions on what’s accepted and how to implement features here. I keep testing things. Sorry. But the goalposts also seem to constantly be shifting. Embedding a .gif works one way, I do it again and then it fails. Let’s try using a freeware TinyTake .gif stored online.

    page link:
    page link saved as URL link:
    embed link: <video width=”90%” height=”90%” controls autoplay><source src=”″ type=”video/mp4″>Your browser does not support the video tag.</video><br /><a href=”” title=”Powered by TinyTake Screen Capture”>Powered by TinyTake Screen Capture</a>

    direct link:
    direct link saved/entered as URL link:

    How about the Skeptical Science widget URL:

    From the orignial source, 4 Hiroshima bombs per second:

    Maybe one method will work? LOL. And be visible? LOL. Dunno, but not showing anything embedding in my comment preview… so… prospects aren’t good. Magic 8-Ball says, “Don’t count on it.”

  8. This is not a test. I am real. Good morning.
    Dropped by Tuesday when things were just getting started. So happy to finally see this blog rolling. Been missing the information and the characters.

    We do have a hot rod of a season.

  9. Wind shear trough Isaias is going to be traveling through has considerably shrunk. Anti-cyclone to the SW has been steadily eroding the trough and providing a shield to allow Isaias to grow considerably faster than was thought a day ago. With the center going through the Mona passage, we’ll find out shortly if the shear will be a big disruption to intensification. Storms overperforming and hitting major populations is something we can all do without. The fanning on the west side of the massive system is suggestive that shear is not as high as the second map pictured shows. 200mb map, first pictured, shows the true shear is in the Bahamas. Isaias is likely to become a hurricane today or tomorrow, before we find out in roughly two days, how much affect the shear will have. Shear tendency map shows an hourglass like shrinking forming in this shear trough, this is forming in the path that Isaias will take, suggestive that shear may not be the issue to the extent we hoped it would be.

  10. I keep trying to start conversations here – any conversations. But to almost no success. I think this commenting platform fails. If one doesn’t see this within the first page of (30-ish) comments, then it’s gone. And hard to track any future responses anyway.

    Has anybody read Dana Nuccitelli’s nice new YCC article?

    Mr. Nuccitelli is likely an already known author to some. He’s also a climate blogger for The Guardian and Skeptical Science. He’s written a book (2015) Climatology Versus Pseudoscience: Exposing the Failed Predictions of Global Warming Skeptics. Taught a course at University of Queensland (Australia) titled Making Sense of Climate Science Denial. Even more articles penned by Dana Nuccitelli are at: The Bulletin of Atomic Scientists.

    This is one highly nuanced topic on the dynamics of our extreme climate crisis, politics, and policy. Great info on a very different slant for how economics play such an integral role in the failure to act, embolden and self-justify preexisting systems, and continue to kick the can down the road.

    Your thoughts?

    1. Good point you have Carmot, i believe the majority is still commenting on Cat6 mainly because the blog here isn´t working that smoothly yet indeed it´s hard to keep track of comments on here because you have to refresh the page to see new comments , i hope that is going to change any time soon. BTW Thanks Dr. Jeff for the update on PTC 9.

    2. Change does not come easily to many. Though Yale has got this up and running better than most could have hoped for, most the volume is at the old house still. I would say out of respect to Jeff, Bob, and Yale, we should all be over here supporting the new digs. Yet Jeff said opine there until all is ready at YCC. The steps taken have been very impressive Yale, thank you! A longer comment thread so more responses could happen would be cool. The brightness of the old blog really invites you in, all this needs is to be a little more bright and inviting. When the mainstay commenters come on over, then the rest will follow.

      1. Yes, thanks. And fully agree. I’m trying here at YCC. To learn, to (possibly?) be able to explain to others. Like what methods work for embedding an image, etc. IBM/Weather Co. far surpassed my limited expectations by leaving comments open and I understand why Dr. Masters said to remain there. However, without much traffic or beta testing or feedback here…

        How can we all expect it to improve? As just one member of this community, I’m trying to do what I can. I think… Cheers.

      2. It’s coming together fast, this is well ahead of the curve of what most expected. Look at you being the traffic, beta testing, and feedback all in one :). I’d bet this place is amazing with those concerns addressed fast. I think it’s pretty amazing they’ve got this up to this extent; being it’s such a hard format to get right for many reasons.

    3. Thanks for the link.

      About this comment section: Give it time. More features will roll out and more people will be eager to come here I think. Some features I would like added are: Automatic updates of new comments with notifications, embedding of Twitter posts and an improved experience when browsing with a phone.

      1. Yes, all those features. And I agree, I’m trying to be patient. Really, I am. But this platform is also so lacking, it’s stressing me out. Plus I’d like a way to at least view my own previous comments – to track whether any responses have been made. And see others’ previous comments. Of course, with a privacy setting that extends beyond Disqus’ “public” or “private,” I’d wish for a “whitelist” where I could choose those who I’d allow to view all my previous comments.

      2. Yes, thanks. I’ve refrained from input/feedback/suggestions so far. Let them assess, experience, etc. Allow them some time, I think it’s fair. Though, I think their initial rollout had almost no pre-thought as to actualized user experience and needs. Cheers.

    4. It is amazing how a few differences can create a tool that can either facilitate conversation or allow it to fade off into nothingness.

      A lot of this comes down to updating as new information comes in. Cat 6 had ‘live’ updating that allowed you to see when responses came in. All you needed to do was to click on them to see the contents. I am not sure that WordPress allows this, but I think that putting the links to the pages at the top as well as the bottom of the comments page would be a good start as you could immediately tell where you were in the conversation when you arrived.

      It sounds like a new comment engine will show up in November, so hopefully notes are being taken in these first days of interaction.

      You only get one first impression and beginners eyes are the most valuable when it comes to interface testing.

      1. All cogent points, thanks Bob. But I don’t think NewsPack has its own comment software or platform at all. They may choose to shift to Coral Project or Disqus when they migrate to NewsPack, but that’s still a different decision (from moving to NewsPack itself as a CRM and such).

Comments are closed.