Tropical Depressions 13 and 14
Triple trouble: Tropical Depression 14, Tropical Depression 13, and a new tropical wave emerging from the coast of Africa, as seen at 11:20 a.m. Thursday August 20, 2020. (Image credit: NOAA/RAMMB)

Tropical Depression Thirteen (TD 13), which formed in the central Atlantic on the evening of Wednesday, August 19, poses a threat as a tropical storm this weekend to the Leeward Islands, Virgin Islands, and Puerto Rico. TD 13 could affect the Bahamas and Florida as a hurricane on Sunday and Monday, respectively. A Tropical Storm Watch was up for most of the northern Leeward Islands on Thursday.

At 11 a.m. EDT Thursday, August 20, TD 13 was located about 750 miles east of the northern Leeward Islands and headed west-northwest at 21 mph. Conditions for development were favorable, with sea surface temperatures (SSTs) near 28 degrees Celsius (82°F) and light wind shear of about 5 knots. However, the system had moved into a drier region of the atmosphere, with a mid-level relative humidity of 60%, and this dry air was interfering with development. Satellite images showed TD 13 with a modest amount of heavy thunderstorm activity slowly growing in organization and areal coverage.

Figure 1
Figure 1. Visible GOES-16 satellite image of TD 13 at 11:20 a.m. EDT Thursday, August 20, 2020. (Image credit: NOAA/RAMMB)

Heavy rain threat to Leeward Islands, Virgin Islands, Puerto Rico

A west-northwest motion will take TD 13 through or just north of the Leeward Islands Friday evening through Saturday, and the system is predicted to bring the islands 1 – 3 inches of rain, with isolated amounts up to 5 inches. The Virgin Islands and Puerto Rico are likely to see higher rainfall amounts of 3 – 6 inches through Sunday. With the islands on the weaker (left) side of TD 13’s circulation, wind damage should be limited. For a fast-moving system like TD 13, winds on the right (north) side likely will be at least 20 mph higher than those on the left (south) side.

Figure 2
Figure 2. Predicted path of TD 13 from the 6Z Thursday, August 20, 2020, run of the operational GFS model (black line) and its 21 ensemble members (colored lines, which show minimum central pressure). Model members showed a significant threat to the Bahamas and Florida, with about one-third of them showing TD 13 developing into a hurricane. (Image credit: Tropical Tidbits)

The Bahamas and Florida at highest risk early next week

Assuming that TD 13 develops into a tropical storm and does not remain weak, a more northerly track is likely, which would keep the system north of the high mountains of Hispaniola and Cuba. On that track, the Turks and Caicos Islands, Bahama Islands, and Florida are at highest risk of impacts early next week. The Bermuda high, which is steering TD 13, will be strong and will extend far to the west, though a weakness in the high may allow TD 13 to turn more to the northwest on Monday, when it will be near Florida. At that time, TD 13 may have to contend with higher wind shear from a trough of low pressure over the U.S., which might interfere with intensification. Until that time, wind shear is predicted to be a light to moderate 5 – 15 knots. Ocean temperatures will steadily warm over the next five days, reaching a very warm 30 – 31 degrees Celsius (86 – 88°F) by Monday. Warm waters extend to great depth over the Bahamas, giving the ocean a high heat content ideal for fueling rapid intensification.

A NOAA hurricane hunter aircraft is scheduled to investigate TD 13 Thursday evening. The aircraft will be feeding data from its Doppler radar in real time to the HWRF model, the only model currently configured to use this important source of extra data to make forecasts.

Most top intensity models predict TD 13 will become major hurricane and threaten Florida

The five main intensity models used by NHC are the regional/dynamical HWRF, HMON, and COAMPS-TC models (which subdivide the atmosphere into a 3-D grid around the storm and solve the atmospheric equations of fluid flow at each point on the grid), and the statistics-based LGEM and DSHP models. Two of the top-performing global dynamical models for tracking hurricanes – the European (ECMWF) and GFS models – typically are not considered by NHC forecasters when making intensity forecasts, and both generally make poor intensity forecasts.

Figure 3
Figure 3. Skill of computer model intensity forecasts of Atlantic named storms in 2019, compared to a “no skill” model called “Decay-SHIFOR5” that uses just climatology and persistence to make a hurricane intensity forecast (persistence means that a storm will tend to maintain its current behavior). OFCL=Official NHC forecast; GFS=Global Forecast System model; HMON=Hurricanes in a Multi-scale Ocean-coupled Non-hydrostatic regional model; HWRF=Hurricane Weather Research and Forecasting model; Euro=European Center for Medium-range Weather Forecasting (ECMWF) model; COAMPS=COAMPS-TC regional model; LGEM=Logistic Growth Equation Model; DSHP=Statistical Hurricane Intensity Prediction Scheme with inland decay. (Image credit: 2019 National Hurricane Center Forecast Verification Report)

In 2019, the official NHC forecast did the best job predicting intensity, except for 5-day forecasts, which the COAMPS-TC model did a better job at. (See this review I wrote on hurricane model performance in 2019 for Yale Climate Connections.) Thus, NHC’s four-day and five-day intensity predictions that TD 13 will be a category 1 hurricane on Monday, when it makes its closest approach to Florida, is worth respecting. However, it is concerning that the 6Z Thursday run of the COAMPS-TC model, which outperformed the official NHC forecast at 5-day forecasts last year, predicted a category 3 hurricane as of Monday, August 24. In addition, two of the other top intensity models, the HWRF and HMON, also were predicting that TD 13 would be a category 3 hurricane on Monday. The other top intensity models, the LGEM and DSHP models, were predicting that TD 13 by then would be no more than a strong tropical storm.

Bottom line: the official NHC forecast of a category 1 hurricane near Florida on Monday has high uncertainty, but residents should anticipate that TD 13 could be a major hurricane that will hit Florida that day. That said, it is also possible TD 13 could be a disorganized tropical storm at that time, if significant land interaction with Cuba and Hispaniola occur.

Figure 4
Figure 4. The 6Z Thursday, August 20, 2020 forecast of the COAMPS-TC model, which made the best 5-day intensity forecasts in 2019. The model predicted that TD 13 would be a category 3 hurricane on Monday near the coast of Florida. The COAMPS-TC was the third-best track model in 2019, behind the European model and UKMET model. (Image credit: Naval Research Laboratory)

The next two names on the Atlantic list of storms are Laura and Marco. The earliest twelfth storm in Atlantic tropical history was Luis on August 29, 1995. There is a tie for earliest thirteenth storms, with Lee on September 2, 2011, and Maria on September 2, 2005. (Lee was originally the twelfth storm of the 2011 season, but an unnamed system that reached tropical storm strength on September 1, just before Lee, was discovered in post-season analysis.)

Figure 5
Figure 5. Visible GOES-16 satellite image of TD 14 at 10:20 a.m. EDT Thursday, August 20, 2020. (Image credit: NOAA/RAMMB)

Tropical Depression 14 forms in the central Caribbean

A tropical wave in the central Caribbean, which NHC earlier this week designated 97L, developed into Tropical Depression Fourteen (TD 14) at 11 a.m. EDT Thursday, August 20. TD 14 was headed west at 21 mph with top winds of 35 mph, and a Tropical Storm Watch was posted for the northern coast of Honduras.

Dry air, which had been the bane of this system earlier this week, had diminished on Thursday morning, and TD 14 was in a relatively moist atmosphere with a mid-level relative humidity of 65%. Conditions for development were favorable, with SSTs near 29.5 degrees Celsius (85°F) and light wind shear of 5 – 10 knots. Satellite images showed that TD 14 had an impressive amount of heavy thunderstorm activity steadily growing in areal coverage and organization. An Air Force hurricane hunter aircraft is scheduled to investigate TD 14 Thursday afternoon.

Forecast for TD 14

As TD 14 progresses west-northwestward through Saturday, its forward speed will slow as a result of the steering influence of a large trough of low pressure over the central U.S. The upper-level southwesterly winds ahead of this trough will turn TD 14 more to the northwest, and the system is likely to pass over Mexico’s Yucatan Peninsula on Saturday night and enter the Gulf of Mexico on Sunday.

Approaching the Yucatan Peninsula on Friday, TD 14 will find very favorable conditions for development. The 12Z Thursday run of the SHIPS model predicted that the atmosphere surrounding the system would moisten to a relative humidity of 75%, wind shear would be a light 5 – 10 knots, and SSTs would be a very warm 30 degrees Celsius (86°F). The waters of the western Caribbean have the highest heat content of any place in the Atlantic, providing ample fuel for any tropical cyclone that passes across. These conditions likely will allow TD 14 to be near category 1 hurricane strength at landfall Saturday in the Yucatan Peninsula.

Crossing the Yucatan will weaken TD 14, and it may take a day for the storm to reorganize over the warm waters of the Gulf of Mexico, where SSTs are a very warm 30 degrees Celsius (86°F). An upper-level trough of low pressure over the Gulf at that time will bring dry air and high wind shear to TD 14, limiting how much re-intensification can occur. The long-range intensity forecast is uncertain, but TD 14 could be a strong tropical storm or a category 1 hurricane when it makes its expected landfall on Tuesday along the U.S. Gulf Coast.

Figure 6
Figure 6. Visible MODIS satellite image of a tropical wave that emerged from the coast of Africa on Thursday morning, August 20, 2020. (Image credit: NASA Worldview)

Next up: a new tropical wave off the coast of Africa

A strong tropical wave located near the coast of Africa on Thursday morning has the potential to develop into a tropical depression this weekend or early next week. The disturbance will move west-northwest at 15 – 20 mph over the tropical Atlantic, passing to the north of the Lesser Antilles Islands around Wednesday, August 25. In an 8 a.m. EDT Thursday Tropical Weather Outlook, NHC gave the new African tropical wave two-day and five-day odds of formation of 20% and 40%, respectively.

Hurricane Genevieve scrapes the Baja Peninsula

Still clinging to Category 1 strength, Hurricane Genevieve passed dangerously close to the southern Baja Peninsula of Mexico on Thursday, August 20. As of 8 a.m. PDT Thursday, Genevieve was centered about 50 miles southwest of the peninsula, about halfway between Magdalena Bay and Cabo San Lucas and moving northwest, parallel to the peninsula, at 12 mph. The center’s closest approach to land may be when it passes just west of Magdalena Bay and the town of Puerto San Carlos on Thursday afternoon before angling slightly toward the open northeast Pacific.

The most reliable hurricane models, according to their 2019 performance

Intense rainbands were pushing across the southern Baja Peninsula on Thursday. Widespread 2 – 4 inch rains are expected, with a foot or more possible at higher elevations. Sustained winds could briefly hit tropical storm strength (39 mph or more). At 8 a.m. PDT, winds were 25 mph at the Cabo San Lucas International Airport, and 28 mph at the Manuel Marquez de Leon International Airport in La Paz.

Genevieve has weakened steadily since attaining its peak category 4 on Tuesday, August 18. Its track is bringing it over substantially cooler water, and the rugged terrain of the peninsula is disrupting flow around the northeast side of the storm. Genevieve will also be ingesting drier air over time. As a result, further weakening is expected, and Genevieve will likely be a tropical storm by late Thursday and a tropical depression by Saturday.

Bob Henson contributed the Hurricane Genevieve portion of this post.

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Topics: Weather Extremes
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Blainn
Blainn
1 month ago

Joining!

Patrap
1 month ago

Sheesh

sheri parker
sheri parker
1 month ago

I’m glad to be here, but just wondering did they totally take the blog down on WU?

Art
Art
1 month ago

Good Morning

Storm Man
Storm Man
1 month ago
Reply to  Art

Hi art

carmot
carmot
1 month ago

More testing, because where would the world be without tests?
YouTube copy embed code:
<iframe width=”639″ height=”360″ src=”https://www.youtube.com/embed/Y8etd_EWXiU” frameborder=”0″ allow=”accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture” allowfullscreen></iframe>

copy video URL:
https://youtu.be/Y8etd_EWXiU

Standard view URL:
https://www.youtube.com/watch?v=Y8etd_EWXiU

carmot
carmot
1 month ago
Reply to  carmot

Last edited 1 month ago by carmot
carmot
carmot
1 month ago
Reply to  carmot

Last edited 1 month ago by carmot
carmot
carmot
1 month ago

Trying TPW from UCSD servers: https://cw3e.ucsd.edu/satellite/#MIMIC
comment image

carmot
carmot
1 month ago

Himawari-8 infrared URL copy:
comment image
copy image:
comment image
copy image location:
comment image

Last edited 1 month ago by carmot
carmot
carmot
1 month ago
Reply to  carmot

WOOT! All three worked!!!
(from this source page, using the “animated GIF” selections for Himawari-8 30-minute updates): https://www.nhc.noaa.gov/satellite.php

Last edited 1 month ago by carmot
carmot
carmot
1 month ago

Trying to get the MIMIC TPW loop to embed in my comment. Ugh.
HTML5 loop:
http://tropic.ssec.wisc.edu/real-time/mtpw2/product.php?color_type=tpw_nrl_colors&prod=wpac&timespan=24hrs&anim=html5
copy image:
http://tropic.ssec.wisc.edu/real-time/mimic-tpw/wpac/anim/latest72hrs.gif copy image location:
http://tropic.ssec.wisc.edu/real-time/mimic-tpw/wpac/anim/latest72hrs.gif
Save as to computer & uploaded = too large a file size (8.43 mb).

carmot
carmot
1 month ago
Reply to  carmot

Dang, all failed, none worked. I hate this. : (

Mike G.
Mike G.
1 month ago

Can somebody please post the link to the blog posts from Category 6 from WU that are still active? I accidentally closed my tab! Thanks! Still a lot of people posting on that site!

Last edited 1 month ago by Mike G.
Skyepony
1 month ago

Laura impacting the Leeward Islands.
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Skyepony
1 month ago
Reply to  Skyepony

Wow…this hot linked.. @Barefootontherocks

HadesGodWyvern
HadesGodWyvern
1 month ago

09W was named “IGME” by PAGASA

Screenshot_2020-08-21 bulletin pdf.png
HadesGodWyvern
HadesGodWyvern
1 month ago
Reply to  HadesGodWyvern

.

Last edited 1 month ago by HadesGodWyvern
Art
Art
1 month ago

comment image

lg_aatrack[1].jpg
Art
Art
1 month ago

one day i’ll learn how to do this lol

Art
Art
1 month ago

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173715_earliest_reasonable_toa_no_wsp_34[1].png
Chris
1 month ago

Hello. Where is Laura

Tropical fever
Tropical fever
1 month ago

Why all the downvoting? Is someone really that bored?

Barefootontherocks
Barefootontherocks
1 month ago

Dear god(s)
Please send a Knight in white pickup hauling a giant block user button on a flatbed.

Wyatt Washburn
Wyatt Washburn
1 month ago

Kindness is an act
Empathy a choice
Why not be nice
Priceless and comes with no price
If not you can bet when Keep gets that ban button
You’ll have to find a new place to show your butt in

Allright, just tying to do my part for the cause, have a good afternoon, and good luck Mods!

Wyatt Washburn
Wyatt Washburn
1 month ago

I’m sorry anyone had to read the hateful trash that was put out there again and again over the past few days. To not have that removed and the person removed too is hard to fathom. Does no service to Yale nor the Docs. I hope when I come back later this will be resolved. Let me be very clear; the WU I always knew, would never stand for this. Even back when it was the wild west and a lot was allowed, this type of garbage never was. Let’s get them out of here and turn this place into something the Docs and we all can be proud of.

Michael Paul
Michael Paul
1 month ago

What files types are allowable here? jpeg, gif etc…? Thanks in advance.

HadesGodWyvern
HadesGodWyvern
1 month ago
Reply to  Michael Paul

any format can be upload from your computer. Not really sure how well hotlinking images works here.

Michael Paul
Michael Paul
1 month ago
Reply to  HadesGodWyvern

Thank you; been having issues

Wyatt Washburn
Wyatt Washburn
1 month ago
Reply to  Michael Paul

You may be better off asking on the backup blog, lot more there who likely know Michael.

Last edited 1 month ago by Wyatt Washburn
boyznme
boyznme
1 month ago
Reply to  Wyatt Washburn

Where is the back up blog??? Please??

HadesGodWyvern
HadesGodWyvern
1 month ago
Reply to  boyznme
Last edited 1 month ago by HadesGodWyvern
Beantech
Beantech
1 month ago

Afternoon everyone….
Track shifting south and west each run….bodes well for south FL

Michael Paul
Michael Paul
1 month ago

Ok so the most recent comments are at the last page of this Blog. Hope you can rectify soon Doc.

Barefootontherocks
Barefootontherocks
1 month ago
Reply to  Michael Paul

At the bottom of page, click the latest page number and it will reverse order to newest first.

Michael Paul
Michael Paul
1 month ago

Thank U!

Michael Paul
Michael Paul
1 month ago

test twice

Mags
Mags
1 month ago

go away

Michael Paul
Michael Paul
1 month ago

test, again

Wyatt Washburn
Wyatt Washburn
1 month ago

Who trolls in a pandemic, during two possible life threatening storms, as people still dig out from a derecho? California alit, flash flooding in North Carolina, and people hurting in untold ways all over the place. The only downside of everyone being over there is the trolls get to have the run of the place. Typically so busy we ignore the trolls and they use to get popped lighting fast. Let’s hope we get there again soon.

Last edited 1 month ago by Wyatt Washburn
Mags
Mags
1 month ago
Reply to  Wyatt Washburn

I have to try to remember not to acknowledge the less bright. It only encourages them.

Wyatt Washburn
Wyatt Washburn
1 month ago
Reply to  Mags

Their reign of freedom to do this, I’d guess, will come to an end very soon now.

jt53
jt53
1 month ago
Reply to  Wyatt Washburn

An antiscience Breitbart follower and qAnon supporter

rainwalker_3887
rainwalker_3887
1 month ago

So this is where we all are?

Wyatt Washburn
Wyatt Washburn
1 month ago

Scroll down for link to where most are.

Wyatt Washburn
Wyatt Washburn
1 month ago

TD/14 working with anticyclone at least for today. Seperated from the trough over the Southeast for today as well. If TD/14 can take advantage today, and again tonight, tapping those waters it will be traveling over is a real possibility. Trough looking like it’s not hindering too much today, TD/14 should have a good afternoon development wise. As we head into serious times very soon now, I know all sincere hope Yale will give the Mods the tools they need for this place to be of use to the Populace. http://tropic.ssec.wisc.edu/real-time/atlantic/winds/wg8shr.GIF

timothy lane jackson
timothy lane jackson
1 month ago

WHAT HAPPENED TO THESE STORMS.THEY SHOULD BE DEVELOPING THIS TIME OF YEAR.

Skyepony
1 month ago

Tropical Storm Laura
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Skyepony
1 month ago

Strong storms possible for ECFL today..
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Art
Art
1 month ago

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Michael Paul
Michael Paul
1 month ago

Take ur comment and self elsewhere

Mags
Mags
1 month ago
Reply to  Michael Paul

well said Michael Paul !!!

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