Tropical Storm Laura brought torrential rains on Sunday and Monday to the nations of the Dominican Republic and Haiti, which share the island of Hispaniola. The highest 24-hour rainfall amount in the Dominican Republic was 11.70 inches in Barahona, on the southwest coast.

According to weather.com, at least four deaths occurred in the Dominican Republic, where one million customers lost power. In Haiti, a personal weather station in the capital of Port-au-Prince recorded 6.61 inches of rain. Floods in Haiti killed at least nine people, and another two were missing. Laura mostly spared Puerto Rico severe impacts, with 2 – 4 inches of rain falling across the southern portion of the island, but it did knock out power to approximately 100,000 customers in Puerto Rico.

Laura made landfall in eastern Cuba on Sunday night. At 7:51 p.m. EDT Sunday, Guantanamo Bay, Cuba recorded sustained winds of 60 mph, gusting to 72 mph. The base recorded 3.01 inches of rain from Laura through 8 a.m. EDT Monday.

On Monday morning, Laura moved off Cuba and emerged into the waters just south of the island. At 2 p.m. EDT Monday, Laura was located over the waters south of west-central Cuba, about 60 miles from the island. These waters were a very warm 30.5 degrees Celsius (87°F). Laura was headed west-northwest at 21 mph with top sustained winds of 60 mph and a central pressure of 1001 mb.

Radar from the Cayman Islands and Cuba showed that Laura did not have an inner core, and the storm’s spiral bands were not well-organized. However, satellite images late Monday morning showed a steady increase in heavy thunderstorms near Laura’s center, and the storm may be able to build a strong inner core by Monday evening.

Satellite images showed Laura had significantly expanded in size to the south of Cuba and was bringing heavy rains to Cuba, Jamaica, and the Cayman Islands. As of 2 p.m. EDT Monday, a personal weather station in Negril, Jamaica, had recorded 4.97 inches of rain. Wind gusts between 35 and 40 mph were recorded at both Kingston and Montego Bay on Monday morning. Wind gusts between 30 – 45 mph were common in central Cuba on Monday morning.

Laura was a very lopsided storm, with almost all of the heavy thunderstorm activity to the south of Cuba. High-level cirrus clouds were streaming out to the south, indicating good upper-level outflow on that side, but it was more restricted to the north than it had been on Sunday. Laura was embedded in a moderately dry region of the atmosphere, with a mid-level relative humidity of 60%; moderate upper-level wind shear of 10 – 15 knots was affecting the storm, driving dry air into the core and slowing development.

A track just south of Cuba, then into Gulf

Over the next four days, the Bermuda high, which is steering Laura, will be strong and will extend far to the west, forcing the storm generally to the west-northwest. The Monday morning runs of the models indicated that Laura will track just south of Cuba on Monday, with the storm crossing western Cuba and emerging into the Gulf of Mexico early Tuesday morning. If Laura is able to keep its center over water on Monday, it likely will maintain at least its current intensity, and probably strengthen by 5 – 10 mph before emerging into the Gulf of Mexico.

Intensification into strong hurricane likely in Gulf of Mexico

When Laura emerges into the Gulf of Mexico, conditions for intensification are expected to be very favorable. Ocean temperatures are a very warm 30 – 31 degrees Celsius (86 – 88°F) across much of the Gulf of Mexico, and an upper-level high-pressure system with light winds will bring light to moderate wind shear and excellent upper-level outflow. The atmosphere will be somewhat dry, with a mid-level relative humidity of 60%, but with that light wind shear, the dry air is unlikely to significantly impede intensification.

Tropical Storm Marco (see below) will be too small and too far away to bring increased wind shear from its upper-level outflow.

It will take a day or so for Laura to recover after its long struggle with Cuba, but immediately after leaving Cuba behind, the storm is over the warm, deep waters of the Loop Current, with its tremendous amount of ocean heat content (see yesterday’s post), leading Laura to steadily organize. This process may be slowed when Laura encounters a cool eddy in the Gulf on Tuesday afternoon, though, and in addition Laura will have to build up the entire northern portion of its circulation. Laura will expand in size on Tuesday and Wednesday, and will likely grow into a larger-than-average storm capable of generating a very large storm surge.

From Tuesday evening though landfall on Wednesday night, Laura will be passing over Gulf waters with very high heat content, and the top dynamical intensity models – the HWRF, HMON, and COAMPS – continued to predict in their 0Z and 6Z Monday runs that Laura would be at least a category 2 storm, and perhaps at category 4 strength by Wednesday evening, as it approaches landfall in Texas or western Louisiana. The 12Z Monday run of the SHIPS model gave a 24% chance that Laura would rapidly intensify by 65 mph by Wednesday morning, becoming a borderline category 3/category 4 hurricane. The official NHC forecast at 11 a.m. EDT Monday, however, called for a strong category 2 hurricane before landfall.

Where will Laura go?

The model solutions for Laura still have a wide spread, with much of Texas and Louisiana at risk for a potential landfall.

The model trend in recent days has been to build the Bermuda high steering Laura farther to west, pushing the storm more westward, towards Texas. This trend seems to have stabilized a bit, with the models agreeing on a landfall location between the central Texas coast and the central Louisiana coast.

The best-performing model for Laura so far has been the UKMET model, which has out-performed all other models and the official NHC forecast, except for those at 12-hour forecasts. The UKMET model’s 0Z Monday forecast predicted a landfall southwest of Houston, Texas, around 8 p.m. EDT Wednesday as an intensifying hurricane. This model was an outlier among the 0Z Monday guidance, though, and its landfall position lay outside of the NHC cone of uncertainty at 11 a.m. EDT Monday. Update: the 12Z  Monday run of UKMET model had a landfall location near the Texas/Louisiana border, more in line with the official NHC forecast.

The European model ensemble from 06Z Monday also leaned westward of the NHC cone (see below). Note that for about one-third of forecast cones, the actual track will extend outside the cone at some point. The cone is assigned a standard width each year, based on typical errors over the previous five years of tropical cyclones tracks. Some systems end up being less predictable – and some more predictable – than the cone implies. One wildcard in Laura’s future track may be the position of Tropical Storm Marco’s remnants, which may create a weakness in the ridge of high pressure steering Laura, and turn the storm more to the north over the northwest Gulf of Mexico.

Steering currents will keep Laura moving steadily after it comes ashore, so it is unlikely to stall out and produce the type of catastrophic inland rains generated by Hurricane Harvey in 2017. Instead, storm surge and wind are most likely to be the greatest threats posed by Laura.

Residents along the Texas and Louisiana coasts should anticipate the possibility that Laura will rapidly intensify right up until landfall, potentially reaching major hurricane status.

Marco weakens dramatically off Louisiana coast

Tropical Storm Marco, which was briefly a Category 1 hurricane on Sunday in the southern Gulf of Mexico, no longer poses a serious threat to the U.S. coast after being ripped apart by strong wind shear on Monday.

Marco’s small size made it especially vulnerable to the destructive effects of shear and dry air. On Monday, the intense showers and thunderstorms (convection) associated with Marco were being pushed into the Florida Panhandle. Marco’s center of circulation continued to head toward the Louisiana coast, but with virtually no showers and thunderstorms around it. Bereft of the convection needed to support it, Marco’s circulation should weaken rapidly, with a downgrade to tropical depression possible as soon as Monday afternoon or evening.

As of 2 p.m. EDT Monday, Marco was centered about 40 miles southeast of the mouth of the Mississippi River. Top sustained winds were 40 mph, mainly in the convection well east of the storm, near the Florida Panhandle coast. Around Marco’s center, sustained winds were no more than 35 mph, according to surface microwave radiometer data from hurricane-hunter flights. Winds were generally 10 to 20 mph across southeast Louisiana, with gusts to 24 mph at Port Fourchon.

Marco’s weakening center is expected to arc west-northwestward near the Louisiana coast, and it is possible that Marco will not make landfall in the U.S. as a tropical storm, and instead be a tropical depression at landfall. Localized rainfall totals could end up exceeding 5″ in and near the Florida Panhandle, as Marco’s convection is channeled onshore away from the storm center. Lesser rainfall totals could push across far southern Alabama and Mississippi into southeast Louisiana by late Monday. Marco is no longer expected to generate a significant storm surge.

Two U.S. landfalls in a three-day period: a rare occurrence

Assuming that Marco actually ends up making an official landfall, the expected landfall of Laura on Wednesday along the northwest Gulf Coast would give the U.S. two landfalls within a three-day period, a rare occurrence.

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According statistics provided by Dr. Phil Klotzbach of Colorado State University, the U.S. has experienced double landfalls within three days of each other on only 12 other occasions since 1851 – an average of once every 14 years. The most recent double landfall occurred in 2004, when two pairs of double landfalls occurred. Tropical Storm Gaston hit South Carolina at 12Z Aug. 29, and Tropical Storm Hermine hit Massachusetts just 39 hours later. Earlier that same year, Hurricane Charley had hit southwest Florida just 30 hours after Tropical Storm Bonnie had made landfall in the Florida Panhandle.

The shortest time on record between two continental U.S. landfalling hurricanes is the 23 hours that separated Treasure Hurricane (9/4/1933 at 5 UTC) and Cuba-Brownsville Hurricane (9/5/1933 at 4 UTC).

Perhaps the craziest U.S. tropical cyclone onslaught occurred in 1923, when three tropical storms hit the U.S. within a four-day period, between October 16 and October 19.

Editor’s note: Posted August 24, 2020, at 2:02 p.m. EDT. This post was updated at 2:15 p.m. EDT to reflect the latest NHC advisories and the 12Z run of the UKMET model.

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