TS Beryl Forms in Central Atlantic; Typhoon Maria Lashes Guam, Heads For Okinawa

Tropical Depression Two (TD 2) formed on Thursday morning from a tropical wave traversing the waters of the central tropical Atlantic, midway between Africa and the Lesser Antilles Islands. Update: At 2:30 pm EDT Thursday, the National Hurricane Center upgraded TD2 to Tropical Storm Beryl based on satellite data, with top sustained winds estimated at a minimal 40 mph. Beryl is the second named storm of the Atlantic season, but it is expected to weaken back to a tropical wave by the time it reaches the Lesser Antilles Islands on Sunday. The Hurricane Hunters are not scheduled to investigate Beryl until Sunday, since the storm is too far from any land bases for the aircraft to fly out of.

Satellite images early Thursday afternoon showed that Beryl was a small storm, with only a small amount of heavy thunderstorms. The storm was well-organized, though, with a number of low-level spiral bands. The 8 am EDT Thursday SHIPS model forecast diagnosed favorable conditions for intensification, with low wind shear of 5 – 10 knots, a mid-level relative humidity of 65%, and sea surface temperatures (SSTs) near 26.5°C (80°F).

Figure 1. Predicted tracks of Tropical Depression Two from the 0Z Thursday European model ensemble forecast (left) and 0Z Thursday GFS ensemble forecast (right). The tracks from the operational version of the models is shown in red (presumably the best forecast). The purple dots show where the predicted storm is at tropical depression strength, and the blue dots, tropical storm strength. None of the ensemble members predicted that a hurricane-strength storm (light blue dots) would form. The European model ensemble forecasts predict a greater chance that the storm will reach the Lesser Antilles Islands than the GFS ensemble model forecasts do, but both sets of model runs predict that TD 2 will be weakening as it approaches the islands. Image credit: cfanclimate.com.

Forecast for Beryl

The track forecast for Beryl is fairly straightforward, with a ridge of high pressure expected to steer the storm west to west-northwest at 10 – 20 mph over the next four days. The storm will undergo some fluctuations in its forward speed, slowing down from its 16 mph motion it had on Thursday morning to about 10 mph on Friday morning, then speeding up to about 17 mph on Saturday. This motion will bring the storm (or its remnants) into the northern Lesser Antilles Islands on Sunday, and to the Virgin Islands and Puerto Rico on Monday.

Since Beryl is a small storm, it has the potential to undergo more rapid intensity changes than an average-sized storm. Wind shear is expected to remain low through Friday, but not much intensification should occur during this period, since the storm will be tracking over a region of cooler ocean waters with SSTs of 25 - 26°C (77 - 79°F). These temperatures are barely warm enough to support a tropical cyclone. In addition, a large area of dry air associated with the Saharan Air Layer (SAL) lies to the north of Beryl, and it is possible that the storm will pull in some of this dry air over the next few days, slowing intensification.

The big problems for Beryl begin on Saturday, when the storm will encounter a region of high wind shear associated with westerly winds from the subtropical jet stream. At that time, Beryl will also be entering a region of dry air with a mid-level relative humidity near 55%. Ocean temperatures will warm a bit, to 26.5°C (80°F), but the one-two punch of high wind shear and dry air should be able to knock a small storm like Beryl back to tropical wave status by the time it reaches the northern Lesser Antilles Islands on Sunday. Our top models for forecasting hurricane tracks—the European, GFS, and UKMET models—all predicted in their runs from Thursday morning that Beryl would be a tropical wave by Sunday.

Figure 2. Predicted tracks of 96L from the 0Z Thursday European model ensemble forecast (left) and 0Z Thursday GFS ensemble forecast (right). The tracks from the operational version of the models is shown in red (presumably the best forecast). Over 50% of the ensemble members of the European model and GFS model predicted that a tropical depression would form late this week. The purple dots show where the predicted storm is at tropical depression strength, and the blue dots, tropical storm strength. None of the ensemble members predicted that a hurricane-strength storm (light blue dots) would form. The European model ensemble forecasts have the storm coming closer to North Carolina than the GFS ensemble model forecasts do. Image credit: cfanclimate.com.

Tropical depression could develop southwest of Bermuda late this week

An area of low pressure (96L) located a few hundred miles southwest of Bermuda on early Thursday afternoon was headed west-northwest at about 10 mph towards North Carolina, and has the potential to develop into a tropical depression late this week. Satellite loops early Thursday afternoon showed that the system, designated 96L by NHC on Thursday, had a moderate degree of rotation, but its heavy thunderstorm activity was limited and disorganized. Sea surface temperatures (SSTs) in this region are near 28°C (82°F), about 1°C (1.8°F) above average—plenty warm enough to allow the system to become a tropical depression. Wind shear was a light 5 - 10 knots—favorable for development.

The 0Z Thursday operational runs of our top three models for predicting tropical cyclone genesis--the European, GFS and UKMET models—all showed some weak development of this system by Saturday, in the waters between North Carolina and Bermuda. More than 50% of the 50 members of the European model ensemble and the 20 members of the GFS model ensemble also supported this idea. The solutions predicted a northerly track for the storm late this week and into the weekend, keeping it several hundred miles away from the U.S. East Coast. It is possible that the western portion of the storm’s circulation may bring 1 – 2” of rain to North Carolina’s Outer Banks on Saturday and Sunday.

Most of the ensemble members of the 0Z Thursday European and GFS models predicted that this system would remain at tropical depression strength, and none predicted that this would become a hurricane. The storm has until Sunday to get its act together, before a cold front overtakes it and makes further development unlikely. This storm does not look to be a threat to any land areas. In their 8 am EDT Thursday Tropical Weather Outlook, the National Hurricane Center gave 2-day and 5-day odds of development to this system of 30% and 40%, respectively.

Figure 3.  Infrared image from Japan’s Himiwari-8 satellite of Typhoon Maria as of 1320Z Thursday, July 5, 2018 (11:20 pm Thursday in Guam). Image credit: RAMMB-CSU/NOAA/CIRA.

Maria could become a supertyphoon this weekend

After passing just north of Guam as a tropical storm on Thursday afternoon local time, Tropical Storm Maria has muscled its way to typhoon status, becoming the third typhoon of the year in the Northwest Pacific. You may be wondering how we can have a Maria this year, given that the name was permanently retired in the Atlantic following last year’s devastating strike by Hurricane Maria on Puerto Rico. The answer: Each of the world’s ocean basins uses a different set of names for its tropical cyclones, all submitted by the weather agencies that handle forecasts for various regions and approved and maintained by five regional committees of the World Meteorological Organization. There is no rule against a name that's been retired in one basin remaining on the list of another basin. Because Guam is a U.S. territory, Maria marks one of the first times in memory that two storms of the same name have affected U.S. territories in different ocean basins in consecutive years.

As of 11 am EDT Thursday (1 am Friday local time), the Joint Typhoon Warning Center (JTWC) placed the center of Maria about 150 miles west-northwest of Navsta, Guam. Maria had strengthened to a Category 1 equivalent, with top sustained winds of 80 knots (90 mph), and was moving west-northwest over open water at around 8 mph.

Figure 4. Maria made landfall on Guam Wednesday afternoon near 2 pm EDT as a tropical storm with 65 mph winds. The storm was building an eyewall as it hit the island, and brought sustained winds of 58 mph gusting to 95 mph to Andersen Air Force Base between 2 pm and 3 pm EDT Wednesday (4 - 5 am Thursday local time).

Maria has a compact core of intense showers and thunderstorms (convection) with a distinct eye and a sprawling area of spiral bands feeding toward the center, which will provide a healthy framework for intensification. SSTs are expected to remain quite warm along Maria’s path for the next several days, around 29 - 30°C (84 - 86°F), and mid-level relative humidity will average 60 - 70%. Both of these factors will enhance the odds of strengthening despite moderate wind shear of 10 - 20 knots. In its 15Z Thursday update, the JTWC predicted that Maria would peak as a Category 4 equivalent in about 48 hours, with top winds of 125 knots (145 mph)--just short of the supertyphoon threshold of 130 knots. Maria will still be far from any land threat at this point, but its west-northwest track will bring it over Japan’s Kyushu Islands (which include Okinawa) early next week, perhaps in a weakening but still-powerful state. Maria could go on to affect land areas from eastern China to Korea by the middle of next week.

Bob Henson wrote the Typhoon Maria portion of this post.