Turbulence 95 liters gets more organized on the way to the Lesser Antilles -

Turbulence 95 liters gets more organized on the way to the Lesser Antilles

A tropical wave that emerged from the African coast on Wednesday occurred midway between the Lesser Antilles and the coast of Africa on Friday afternoon. The system, designated Invest 95L by the National Hurricane Center, could develop into a tropical depression before moving across the Lesser Antilles and into the eastern Caribbean by Tuesday or Wednesday, though there is a lot of uncertainty.

Satellite imagery showed that 95L had developed a good amount of circulation, but severe thunderstorm activity was suppressed by a large area of ​​dry air to the north associated with the Saharan atmospheric layer. Aside from the dry air, conditions were favorable for development, with light winds of 5-10 knots and warm sea surface temperatures of 28 °C (84 °F).

95L forecast tracks from the European model range.
Figure 1. Tracking forecasts up to 10 days for 95 liters of 0Z on Friday 21 July, EC model run. Individual forecasts for the 51 group members are the lines color-coded by the wind speed in knots they predict for 95 lt; Red colors correspond to a Category 1 hurricane. The time in hours from the time the form was initialized in gray text. (Image credit: weathernerds.org)
95L predicted trajectories from the GFS model suite.
Figure 2. Tracking forecasts up to 8 days for 95 liters of 12Z on Friday 21 July, GFS cluster model run. Individual forecasts for the 31 group members are the lines color-coded by the knot wind speed they predict for 95 lt; Red colors correspond to a Category 1 hurricane. The time in hours from the time the form was initialized in gray text. (Image credit: weathernerds.org)

forecast for 95 liters

95l was slowly moving west at less than 10 mph due to interaction with the near-permanent band of severe thunderstorms to the south called the Intertropical Convergence Zone, or ITCZ. By Saturday, 95l is expected to gain further separation from the ITCZ ​​and begin moving west at 10-15 mph. This movement should take the system across the Lesser Antilles into the eastern Caribbean on Tuesday or Wednesday.

The intensification of 95 liters will depend on whether the system can build a core of severe thunderstorms that can battle the dry air to the north. Because the 95L is such a small system, this process can happen relatively quickly. However, the young system is also vulnerable to sudden turbulence from modest increases in wind shear. The Friday 12Z wind shear forecast from the SHIPS model is for shear to remain light, less than 10 knots, for the next six days, but the GFS model, the European model and their combinations didn’t offer much support for the 95l’s development. The European 0Z Friday model group included the operation of 10 of the 51 of its members who developed a 95L into a tropical depression (and four of those who predicted an eventual hurricane). Friday’s 12Z of the GFS model group has eight of its 31 members developing 95 gal into a tropical depression or tropical storm but none of them predicting a hurricane.

At 2 p.m. EDT Friday in the Tropical Weather Forecast, the National Hurricane Center gave 95 hurricanes two-day and seven-day development odds of 40% and 60%, respectively. This was a significant 20% increase over the odds given six hours earlier. The next name on the list of storms in the Atlantic Ocean is Emily. The Hurricane Hunter is scheduled to start at 95L on Monday afternoon.

Update (11 p.m. Saturday): The odds of developing 95 liters for two and seven days are 40% and 50%. The system hasn’t noticeably regulated since Friday.

Tropical Storm Dawn continues to roam through the Central Atlantic Ocean

A week after it formed on July 14, the tropical storm is still raining down across the remote mid-Atlantic without posing a threat to any land areas. At 11 a.m. EDT Friday, Don had sustained winds of 50 mph and was moving west-northwest at 10 mph. Don is close to completing a roughly 360-degree clockwise cycle over the open ocean and is expected to weaken quickly Sunday after moving north of the relatively warm waters of the Gulf Stream. Don is expected to become a post-tropical cyclone Monday over the cool Atlantic waters east of Newfoundland, Canada, and will not pose a threat to any land areas.

Update (11 p.m. Saturday): Don unexpectedly strengthened to hurricane strength Saturday afternoon, becoming the first hurricane of the 2023 Atlantic season. On average, the first hurricane of the Atlantic season arrives on August 11. Don attained hurricane strength at the unusual poleward latitude of 40.1 degrees north, above a warm oceanic gyre bulging north from the Gulf Stream.

At 11 p.m. Saturday, it’s still below the slightest Category 1 winds of 75 mph. However, Don is expected to weaken quickly on Sunday and become posttropical as it passes over cooler waters.

Tropical Depression Doksuri satellite image.
Figure 3. An infrared satellite image of Tropical Depression Duxuri as of 1:10 p.m. EDT on Friday, July 21, 2023. (Image credit: RAMMB/CIRA/CSU)

Duxuri may threaten Taiwan as a strong typhoon

Tropical Depression Duxuri gained strength Friday in the northwest Pacific Ocean and is set to head northwest as a powerful typhoon, possibly swinging over or near Taiwan. Doxuri’s highest sustained winds were at 35 mph as of 11 a.m. EDT, according to the Joint Typhoon Warning Center. The center expects Duxuri to intensify steadily over the weekend, reaching typhoon strength by Sunday as it drifts west, and then reaching Category 3 strength by midweek, when it should accelerate to the northwest and approach Taiwan. The Philippine Weather Agency Pagasa (which names the storm as Ijay) on Friday forecast Typhoon Doxuri to reach super typhoon strength (150 mph sustained winds) as it approaches Taiwan. The GFS and European models were much less optimistic than the EAs, but that may simply be because the system is not yet sufficiently structured for these global models to visualize it well.

Update (11 p.m. Saturday): The models are now converging on a serious typhoon threat to Taiwan, especially the southern parts of the island. Most members of the European Model Teams and GFS Doksuri bring northern Philippines, with a number of group members (particularly GFS) projecting a path that would put southern Taiwan into the more dangerous northern part of Doksuri, including potential landings, around the middle of the week. The new high-resolution HAFS-A model was forecasting landfall in southern Taiwan at Category 4 strength late Wednesday.

As with many systems in the Pacific Northwest, Doksuri is surrounded by a large field of tropical moisture, with showers and thunderstorms (convection) already widespread but disorganized. Wind shear should be relatively modest around Duxuri over the next several days, and the storm will pass over very warm waters, with sea surface temperatures near 29-30 °C (84-86 °F), close to average for this time of year. The oceanic heat content deeper under the Doksuri track will be very high early next week. Given these factors, it wouldn’t be surprising to see the storm embark on a period of rapid intensification once it becomes more structured, perhaps on Sunday or Monday.

Upper level flow is expected to remain somewhat weak around Doksuri in the coming week, so the storm may move farther north before reversing east. This means that we will need to watch for potential impacts later in the week towards eastern China, Korea and Japan.

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