Converging storms image
Converging storms: Hurricane Center's wind speed probability map at 11 a.m. EDT Friday, August 21, 2020, shows Tropical Storm Laura and Tropical Depression 14 converging in the Gulf of Mexico on Tuesday, August 25, 2020. Both systems were predicted to be strong tropical storms or category 1 hurricanes in the Gulf on Monday and Tuesday. (Image credit: National Hurricane Center)

Tropical Storm Laura formed in the waters just east of the Leeward Islands at 9:05 a.m. EDT Friday, August 21, 2020, making it the earliest twelfth storm on record for an Atlantic hurricane season. The previous record was held by Luis on August 29, 1995.

Laura poses a threat as a tropical storm this weekend to the Leeward Islands, Virgin Islands, and Puerto Rico, where Tropical Storm Warnings were posted. A more southerly predicted track lessens the threat early next week to the Bahamas and the Florida east coast, but increases the threat to Hispaniola and Cuba.

Figure 1
Figure 1. Radar image from the Guadeloupe radar of Tropical Storm Laura at 11:30 am EDT Friday. Heavy rains were affecting the Leeward Islands, particularly Guadeloupe and Dominica. (Image credit: Meteo France)

At 11 a.m. EDT Friday, August 21, Laura was located about 210 miles east-southeast of the northern Leeward Islands. Laura was headed west at 18 mph, with top sustained winds of 45 mph and a central pressure of 1007 mb. The storm was experiencing more upper-level wind shear than on Thursday: a moderate 10 – 20 knots. More detrimental to Laura was wind shear occurring at middle levels of the atmosphere, where strong east-northeasterly winds moved in opposition to the low-level flow out of the southeast. This mid-level shear was causing Laura to suffer misalignment, with the low-level center considerably to the northwest of the circulation center at mid-levels.

On Friday morning, the Hurricane Hunters found that Laura’s surface center had relocated farther to the south, closer to the mid-level center. This better alignment of the storm was reflected in an improved satellite presentation, as a modest amount of heavy thunderstorm activity slowly grew in intensity, organization, and areal coverage. High level cirrus clouds streaming away from Laura to both north and the south showed the storm was establishing upper-level outflow, a sign of increased organization.

Sea surface temperatures (SSTs) were favorable for development, near 28 degrees Celsius (82°F), but Laura was embedded in a moderately dry region of the atmosphere, with a mid-level relative humidity of 60%. The wind shear dogging Laura was injecting dry air into the circulation, interfering with development.

Figure 2
Figure 2. Visible GOES-16 satellite image of Laura at 11:20 a.m. EDT Friday, August 21. (Image credit: NOAA/RAMMB)

Laura primarily a heavy rain threat to the islands

Laura is primarily a heavy rain threat to the islands in its path, with the Virgin Islands, Puerto Rico, and Hispaniola (shared by the Dominican Republic and Haiti) likely to receive 3 – 6 inches of rain with isolated higher amounts. For the islands on the weaker (left) side of Laura’s circulation, wind damage should be limited. For a fast-moving system like Laura, winds on the right (north) side likely will be at least 15 mph higher than those on the left (south) side.

Figure 3
Figure 3. Predicted path of Laura from the 6Z Friday, August 21, 2020, run of the operational GFS model (black line) and its 21 ensemble members (colored lines, which show minimum central pressure). Only three of the model members showed Laura developing into a hurricane. (Image credit: Tropical Tidbits)

A more southerly track predicted

Laura did not develop into a tropical storm as early as models had originally predicted, and its center has reformed farther to the south. As a result, the Friday morning runs of the models predicted a more southerly track for Laura than they did previously. A more southerly track increases the odds that the system will encounter disruption from the islands of Puerto Rico, Hispaniola, and Cuba. The 0Z Friday runs of the European, GFS, UKMET, and HMON models all predicted that Laura would encounter significant disruption by these islands. The HWRF and COAMPS-TC models kept Laura just north of the islands, and both of these models predicted that Laura would become a major hurricane in the Gulf of Mexico on Tuesday after passing along the north coast of Cuba and through the Florida Keys on Monday. The 6Z Friday runs of these two models were similar. The HWRF model had the advantage of initializing its forecast with Doppler radar data from Thursday night’s NOAA P-3 hurricane hunter mission, something no other model ingests.

The Bermuda high, which is steering Laura, will be strong and will extend far to the west, steering the storm generally to the west-northwest over the next five days. A weakness in the high will allow Laura to turn more to the northwest on Monday, when it should be near the Florida Keys. At that time, Laura may have to contend with higher wind shear from a trough of low pressure over the U.S., which might interfere with intensification. Laura may also have to contend with increased wind shear resulting from the upper-level outflow from Tropical Depression 14, which is expected to be in the northwest Gulf of Mexico on Tuesday (see below). Until that time, upper-level wind shear for Laura is predicted to be a light to moderate 5 – 15 knots. However, strong mid-level wind shear will likely still be a problem for the storm through Saturday.

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 across the Bahamas, giving the ocean a high heat content ideal for fueling rapid intensification. The main detriment to Laura’s intensification beginning on Saturday will be interaction with land.

NOAA hurricane hunter aircraft will continue to investigate Laura though the weekend, feeding data from their Doppler radars in real time to the HWRF model. The NOAA jet is to make its first mission into Laura on Friday evening. Data from the dropsondes launched by the NOAA jet have been shown to improve track forecasts by as much as 15%.

Figure 4
Figure 4. Visible GOES-16 satellite image of TD 14 at 11:20 a.m. EDT Friday, August 21, 2020. (Image credit: NOAA/RAMMB)

Tropical Depression 14 struggling in western Caribbean

Tropical Depression Fourteen (TD 14) was struggling to organize in the western Caribbean on Friday because of dry air and land interaction. At 11 a.m. EDT Friday, August 21, the center of TD 14 was located off the north coast of Honduras, about 325 miles southeast of Cozumel, Mexico. TD 14’s close proximity to land was inhibiting the flow of moist air into the system, which was headed northwest at 14 mph, away from the coast, favoring development.

Although the pockets of dry air in the western and central Caribbean interfere with its development, TD 14 was in a relatively moist large-scale environment, with a mid-level relative humidity of 70%. SSTs near 30 degrees Celsius (86°F) and light wind shear of 5 – 10 knots favored development. Satellite images showed that TD 14 was still disorganized, and had only modest heavy thunderstorm activity.

Figure 5
Figure 5. Predicted path of TD 14 from the 6Z Friday, August 21, 2020, run of the operational GFS model (black line) and its 21 ensemble members (colored lines, which show minimum central pressure). No model member predicted TD 14 would attain a pressure less than 990 mb, the type of pressure typically seen in a strong tropical storm. (Image credit: Tropical Tidbits)

Forecast for TD 14

As TD 14 progresses 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 take TD 14 to the northwest over Mexico’s Yucatan Peninsula on Saturday night, and into the Gulf of Mexico on Sunday.

Approaching the Yucatan Peninsula on Saturday, TD 14 will find very favorable conditions for development. The 12Z Friday run of the SHIPS model predicted that the atmosphere surrounding the system would be a moist 70 – 75%; wind shear would be a light 5 – 10 knots; and SSTs would be a very warm 30 – 30.5 degrees Celsius (86 – 87°F). These conditions are expected to allow TD 14 to be a strong tropical storm at landfall Saturday evening 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 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.

The next name on the Atlantic list of storms is Marco, the thirteenth named storm of 2020. There is a tie for record-earliest thirteenth storm of the season, 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.)

Will Laura and TD 14 perform a Fujiwara dance in the Gulf of Mexico?

When two tropical cyclones approach within about 900 miles of each other, they tend to rotate counter-clockwise around a common center, then go their separate ways, in a process called the Fujiwara effect. In rare cases they may merge into one storm, but the resulting storm will not be stronger than either of the original two storms, since wind shear from each weakens the other. More commonly, when two storms interact, one will weaken or destroy the other with its wind shear, just as Hurricane Wilma did to Tropical Storm Alpha in 2005.

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Some model runs have shown that Laura and TD 14 may be of similar strength and less than 900 miles apart in the Gulf of Mexico on Tuesday, resulting in a Fujiwara interaction. The 0Z Friday run of the German ICON model showed this, with TD 14 slowing its approach to the Texas coast as a result of its rotating counter-clockwise around a common center with Laura.

A new tropical wave off coast of Africa has potential to develop

A strong tropical wave located near the coast of Africa on Friday morning has some modest 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 and bring heavy rain showers and the threat of flash flooding to the Cabo Verde Islands over the weekend. The 0Z Friday operational runs of the GFS, European, and UKMET models did not show development of this wave during the coming five days. In an 8 a.m. EDT Friday Tropical Weather Outlook, NHC gave the new African tropical wave two-day and five-day odds of formation of 20% and 40%, respectively.

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Jeff Masters

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...

395 replies on “Tropical Storm Laura and Tropical Depression 14 predicted to converge in Gulf of Mexico”

  1. Watching the PR radar today has been fascinating. The old MLC has come ashore east of Ponce, while the old surface low as marked by NHC has been pretty stationary SW of Ponce with a lot of new convection firing in the area. But I can’t tell of that convection is truly rotating locally or behaving more as a new feeder band for the old MLC circulation. Either way, Laura looks vigorous today, with lots of moisture, so it makes me think it will survive for many days.

  2. Well, I’ll have the gopro running when this starts to head this way. I’m in Delcambre, LA and it looks like Laura has us in her sights while Marco is going to push some water up the canal. 2020 has jokes and unfortunately they’re not the funny variety

  3. Is there some reason I can’t get this latest page to resize to fit in portrait mode on my phone? Very annoying.

  4. I see both our storms are undergoing some strengthening. You can already see the outflow from Laura moving quickly towards Marco. Very interesting and some what scarry.

  5. I came here because I had been on the WU blog since Ivan. The tone of this blog is a huge disappointment. KOTG particularly disappointing. I

    1. sorry seems some trolling was occurring and I may have been particularly harsh its not my intent but I am only human and tolerate personal attacks on myself for so long

  6. Good day everyone! We will need that shear in the central GOM to hang around more than expected…..Marco seems to be getting better organized…..image via WeatherTap

  7. D+7 forecast for Arctic and California (as it’s pretty much the same all week)

    Wow…here comes the discovery process

    1. Just looked. He’s strengthing and certainly clean thru the chute. And I bet we’ll have a hurricane to deal with by tomorrow.

      Getting up to finish prep shortly.

      Mid Texas Gulf Coast – Matagorda Bay.

  8. Looking at the bigger picture, both storms seem to be moving air in a more circular pattern and from greater distances. They seem less fragile today, with Laura pulling in low level inflow from a long ways, and Marco developing a nice robust if small circulation. Looking at the PR radar, it sure looks like the mid level center will be more likely to pull the old LLC back rather than the opposite. I would bet the MLC becomes the dominant center.

    WTNT63 KNHC 221601
    Tropical Storm Laura Tropical Cyclone Update
    NWS National Hurricane Center Miami FL       AL132020
    1200 PM AST Sat Aug 22 2020
    Recent satellite-derived wind data indicate that the maximum 
    sustained winds in Tropical Storm Laura have increased to near 45 
    mph (75 km/h) with higher gusts. These winds are occurring mainly 
    in a band to the south of Vieques and eastern Puerto Rico. 
    LOCATION...17.8N 67.2W
    Forecaster Pasch
  9. Seems Laura’s future track is still uncertain depending on path according to NHC. ANy chance or more northland shift?

      1. The trough will continue to tilt and likely tomorrow begin to move out on the western front finally. That should send Marco into Louisiana or Mississippi. Things sure are changing fast.

      2. Sorry, said it backwards above, Marco would go more north and east, Laura would go more south and west with that interaction in theory.

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