Jerry Peaks as a Cat 2, Then Weakens; 99L Approaches Windward Islands

September 20, 2019, 11:55 AM EDT

Above: Hurricane Jerry at 11:30 am EDT September 20, 2019. At the time, Jerry was a Category 1 storm with 85 mph winds. Image credit: NOAA/RAMMB.

After peaking as a Category 2 hurricane with 105 mph winds early Friday morning, Hurricane Jerry had weakened to a Category 1 hurricane with 85 mph winds as of 11 am EDT Friday. Data from the Hurricane Hunters and satellite loops late Friday morning showed that Jerry was struggling with high wind shear, which had distorted the symmetry of the hurricane, reduced its amount of heavy thunderstorms, and partially exposed the low-level circulation center to view.

Tropical storm watches are up for portions of the Leeward Islands, since the center of Jerry is expected to pass about 60 – 90 miles to the north of the islands on Friday night and Saturday morning. At 11 am EDT Friday, tropical storm-force winds extended out 45 miles to the south of the center, but this wind field is expected to expand. On Saturday morning, tropical storm-force winds are predicted to extend out up to 80 miles to the southeast. This expansion of the wind field could bring tropical storm conditions to several of the Leeward islands on Saturday morning, particularly Anguilla and Anegada. The bigger danger is heavy rains, though; NHC is warning of isolated rainfall amounts of 4 – 6” in the Leeward Islands, which could cause dangerous flash flooding.

Forecast for Jerry

Jerry was headed west-northwest at 17 mph at 11 am Friday, and this motion is expected to continue for the next few days, with a turn to the north towards Bermuda this weekend. On this track, Jerry could be a threat to Bermuda on Tuesday. While the Friday morning operational runs of the GFS, European, and UKMET models all agreed on this scenario, about 15% of the 50+ members of the 0Z Friday run of the European model predicted that Jerry would miss recurvature and take a westerly track towards the Gulf of Mexico. With wind shear expected to be moderate to high over the next five days, 15 – 25 knots, Jerry is not expected to intensify into a major hurricane.

Disturbance
Figure 1. A tropical disturbance centered about 200 miles south of Haiti at 11:10 am EDT September 20, 2019. Image credit: NOAA/RAMMB.

Little change to disturbance south of Haiti and the Dominican Republic

A tropical wave centered about 200 miles south of Haiti border early Friday afternoon was spreading heavy thunderstorm to Haiti and the Dominican Republic. Satellite loops on Friday afternoon showed that the disturbance had less heavy thunderstorm activity than on Thursday and did not appear to be growing more organized.

Wind shear was high, near 20 knots, due to strong upper-level winds. This shear was keeping the disturbance disorganized. The disturbance was headed to the west-northwest at about 5 mph into an area of higher wind shear, which makes significant development unlikely. The disturbance will likely bring heavy rains to Haiti and the Dominican Republic Friday and Saturday, and to Jamaica and eastern Cuba on Saturday and Sunday. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10%.

99L
Figure 2. Predicted path of 99L from the 6Z Friday September 20, 2019 run of the GFS model (thick black line) and its ensemble members (thin lines). 99L was predicted to take a path through the Windward Islands on Sunday, then turn north and move over Puerto Rico by Tuesday. Image credit: tropicaltidbits.com.

Tropical wave 99L approaching Windward Islands may develop

A tropical wave located about 700 miles east of the Lesser Antilles Islands at 8 am EDT Friday was headed west at about 20 mph. This disturbance was designated Invest 99L by NHC on Friday morning. Satellite images on Friday morning showed that 99L had a moderate amount of heavy thunderstorm activity, but the system was poorly organized, had little spin, and was struggling with dry air. Wind shear was moderate, near 15 knots, and SSTs were warm, near 29.5°C (85°F).

The fast forward motion of 99L will bring it into the Windward Islands on Sunday, when wind shear is predicted to rise to the high range, 20 – 25 knots. This will likely slow or halt development. 99L had support for development by early next week from about 50% of the 21 members of the 0Z Friday GFS model ensemble forecast, but only about 10% of the 50+ members of the 0Z Friday European model ensemble. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave 99L 2-day and 5-day odds of development of 20% and 30%, respectively. Once 99L reaches the Eastern Caribbean on Monday, it will likely slow down and turn to the northwest, following a weakness in the ridge of high pressure to its north caused by the passage of Hurricane Jerry. Puerto Rico and the Dominican Republic could see rain from 99L as early as Tuesday. A hurricane hunter aircraft is on call to investigate 99L on Saturday, if needed.

New African tropical wave may develop early next week

A tropical wave expected to emerge from the coast of Africa on Saturday has support for development early next week by about 50% of the 70+ members of the 0Z Friday GFS and European model ensemble forecasts—as well as the 0Z Friday operational runs of our three reliable models for prediction tropical cyclone genesis. This system is expected to move west then west-northwest later next week. While the latest model runs predict that this will most likely be a “fish” storm that will not affect any land areas, it is too early to be making that call yet. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 70%, respectively. The next name on the Atlantic list of storms is Karen.

We'll have an update on the flood disaster in Texas from Tropical Storm Imelda later today.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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Dr. Jeff Masters

Dr. Jeff Masters co-founded Weather Underground in 1995, and flew with the NOAA Hurricane Hunters from 1986-1990.

jeff.masters@weather.com

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