Jeff Masters Weather Blog

Multiple tropical threats lurking in the Atlantic as July awaits offstage » Yale Climate Connections

The 2022 Atlantic hurricane season is showing every sign of kicking into higher gear as the first half of the year draws toward a close. Over the weekend of June 25-26, the National Hurricane Center was keeping tabs on several disturbances, two already tagged for potential development.

The newer of the two tagged areas is the northwest Gulf of Mexico, with ensemble computer model runs suggesting a disturbance could form early next week along the trailing edge of a weak cold front that was moving across the Mississippi Valley over the weekend. Heavy thunderstorms were developing on Saturday afternoon across the northeast Gulf, and the disturbed weather is expected to migrate west toward the Texas and Louisiana coast by Monday. As evident in Figure 1 below, surface temperatures have been exceptionally warm in this area, running between 85°F and 90°F and pushing night-time lows into record-shattering territory. On June 21, Galveston, Texas, had a sultry low of 86°F—the warmest daily minimum observed there during any June in 149 years of record keeping. As of June 24, Galveston had not dipped below 81°F since June 4.

Computer models project wind shear will be relatively low over the northwest Gulf on Monday and Tuesday beneath an upper-level high. Should a persistent area of thunderstorms emerge on the tail end of the front, it could consolidate into a tropical system, if enough moisture is available to fend off a large area of relatively dry air now covering much of the Gulf.

Only a minority of ensemble members from the Saturday morning runs of the GFS and European models were showing development, and none depicted a strong system. As of 2 p.m. Saturday, NHC was predicting a near-zero chance of development of at least a tropical depression in the Northwest Gulf through Monday, with a 20% chance from Monday through Thursday.

Figure 1. Sea surface temperatures in degrees Celsius as of June 25 (top) and departures from the seasonally averaged SSTs (1981-2010) across the tropical and subtropical North Atlantic. Readings already exceed 30 degrees Celsius (86°F) off the coast of Louisiana, more than 2°C (4°F) above average for late June in some areas. (Image credit:

Agitated weather blossoming across main development region

The other area of key interest remained the main development region (MDR) for hurricanes, between the coast of Africa and Central America, including the Caribbean. Unusually favorable conditions for late-June tropical activity were already in place across much of that area, and complicated interactions may occur between several blossoming systems.

On Saturday afternoon, June 25, a tropical wave in the eastern Atlantic near 8°N, 36°W, designated 94L by the NHC on Friday, was headed west at 15-20 mph. This position close to the equator has been slowing development of 94L, leaving it unable to leverage the Earth’s spin much to help start it spinning. However, the southward displacement has allowed 94L to escape the influence of the dry Saharan Air Layer to the north, and the disturbance otherwise had unusually favorable conditions for development for June, with sea surface temperatures near 28 degrees Celsius (82°F), unusually light wind shear of 5-10 knots, and a moist atmosphere with a mid-level relative humidity of 70%.

Two other disturbances were flanking 94L along the intertropical convergence zone. To the east of 94L, a tropical wave located near 8°N, 53°W actually had more vigorous showers and thunderstorms (convection) than 94L did on Saturday afternoon, as shown in the satellite image at the top of this post.

Toward the east of 94L, yet another wave was centered near 8°N, 20°W, with more limited convection but a distinct mid-level circulation.

Forecast for 94L

The European and GFS models and several of their ensemble members continue to develop 94L into a tropical storm by early next week. Steering currents favor a general west to west-northwesterly track, with the Saturday morning runs of the GFS and European models predicting 94L will enter the Windward Islands of the Lesser Antilles on Tuesday, June 28, or Wednesday, June 29, as a tropical depression or weak tropical storm. Tropical storms and hurricanes in the North Atlantic often angle poleward as they intensify (the beta effect), and this tendency is showing up in the ensemble model forecasts for 94L after it enters the Caribbean. The operational GFS and European runs and most of their ensemble runs keep 94L pushing across the southern Caribbean toward Central America, while a very small number of runs develop a stronger system moving more toward the west-northwest. Any potential movement of 94L into the Gulf of Mexico is more than a week away (i.e., after July 2).

In a 2 p.m. EDT Saturday Tropical Weather Outlook, NHC gave 94L two-day and five-day odds of formation of 30% and 60%, respectively. The first hurricane hunter mission into 94L is tentatively scheduled for Monday afternoon. The next name on the Atlantic list of storms is Bonnie, one of the most recycled names on the rotating list of storms: Seven previous incarnations of Bonnie have appeared, beginning in 1980.

Figure 2. Tracks of all tropical cyclones in the NOAA database (1851-2021) that have developed or moved across the eastern Caribbean and the Main Development Region of the tropical Atlantic. (Base image credit: NOAA Historical Hurricane Tracks.)

An unusual June threat for the Lesser Antilles and eastern Caribbean

Across the 172 years of Atlantic hurricane records kept by NOAA, only four tropical storms have been known to develop in the MDR during June: an unnamed 1933 storm, Ana (1979), Bret (2017), and Elsa (2021). Ana and Bret reached the Lesser Antilles as tropical storms and dissipated shortly thereafter. Elsa strengthened into a Category 1 hurricane as it crossed the Windward Islands (becoming the first hurricane to strike Barbados at any time of year since Janet in 1955). It went on to cross the Caribbean and strike Cuba and Florida as a tropical storm, causing an estimated $1 billion in damage along its prolonged path. The 1933 system was the strongest of this small group, striking Trinidad and northeastern Venezuela as a Category 1 on July 2 and making landfalls in western Cuba and northeastern Mexico as a Category 2 hurricane.

Three other June tropical depressions that formed east of the Antilles did not attain named-storm strength (see Figure 2 above).

No tropical cyclone has been known to develop over the eastern half of the Caribbean during the month of June. The eastern Caribbean is notoriously hostile to early-season development, largely because strong vertical wind shear and sinking motion often prevail there during June and July. However, models are projecting considerably less shear than usual in the last several days of June 2022, as both easterly low-level trade winds and westerly upper-level winds are predicted to be weaker than usual.

Early-season storms in MDR a likely harbinger of an active season

A named storm forming in the main development region in June or July is typically a harbinger of an active season, as it shows the atmosphere and ocean conducive for activity. See our June 24 post for more details.

Website visitors can comment on “Eye on the Storm” posts. Please read our Comments Policy prior to posting. Comments are generally open for 30 days from date posted. Sign up to receive email announcements of new postings here. Twitter: @DrJeffMasters and @bhensonweather

Source link