TD 7 Forms in the Eastern Atlantic; Likely to Become Tropical Storm Grace

By: Jeff Masters , 3:46PM,GMT on September 5,2015

Tropical Depression Seven spun into life on Saturday morning in the waters a few hundred miles south of the Cape Verde islands in the Eastern Atlantic, and appears poised to become Tropical Storm Grace by Sunday. TD 7 is under conditions which favor development: light wind shear of 5 - 10 knots, warm ocean waters of 28.3°C (83°F), and a moist atmosphere. The farther south TD 7 stays during the coming week, the greater its chances of development, since a strong band of upper-level winds blowing from west to east will lie a few hundred miles to its north, at a latitude roughly even with Puerto Rico. The atmosphere is also drier to the north. The wave is headed nearly due west today, but will gradually assume more of a west-northwest track. The 8 am EDT Saturday run of the SHIPS model predicted that by Wednesday, TD 7 should gain enough latitude to begin experiencing high wind shear of 20 - 25 knots and a much drier atmosphere. These conditions should act to weaken and possibly destroy TD 7 by the time it makes its closest pass by the northern Lesser Antilles Islands on Friday night or Saturday. Penetration into the Caribbean will be difficult for the storm, as the high wind shear which has dominated the region all summer shows no signs of slackening during the coming ten days.


Figure 1. MODIS image of Tropical Depression Seven in the waters of the Eastern Atlantic a few hundred miles south of the Cape Verde islands, taken at approximately 8:15 am EDT Saturday, September 5, 2015. Image credit: NASA.

Fred hanging on
Persistent Tropical Storm Fred continues to mill about in the waters of the Eastern Atlantic as a minimal-strength tropical storm with 40 mph winds. High wind shear will affect Fred through Monday, keeping the storm weak or possily killing it. However, Fred will encounter lower wind shear and anomalously warm waters of 27.5°C (82°F) by Tuesday, and come close to the Azores as a tropical storm on Thursday or Friday.


Figure 2. Hurricane Ignacio is about to get absorbed by an extratropical storm to its north, as seen by Aqua/MODIS on September 4, 2015. Image credit: NASA.

Pacific quieting down
Two tropical cyclones died today over the North Pacific, leaving two others spinning. We lost Hurricane Ignacio Saturday morning, as it got absorbed by a powerful extratropical storm midway between Hawaii and Alaska's Aleutian Islands. The remains of Ignacio may bring heavy rains to British Columbia on Wednesday. Tropical Storm Kevin, off the coast of Mexico's Baja Peninsula, also met its maker Saturday morning, when high wind shear of 35 knots tore away all of Kevin's heavy thunderstorms. Who's left? Well, in the Central Pacific, we still have weakening Category 1 Hurricane Jimena, with top sustained winds of 80 mph at 11 am EDT Saturday. Jimena will likely pass within 500 miles of Kauai in the Hawaiian Islands on Wednesday. However, high wind shear should weaken Jimena to a tropical depression by then, leaving heavy rains the main threat from the storm. Long-lived Category 1 Typhoon Kilo is now in its 16th day as a tropical cyclone, including a long spell as a major hurricane. Kilo is predicted to steadily re-intensify over the weekend, reaching Category 4 strength by Monday as it moves on a westward path that will likely take it several hundred miles north of Wake Island. Kilo is likely to be around until at least September 11, as it passes to the east of Japan.

An area of disturbed weather in the Northeast Pacific located about 550 miles south-southwest of Manzanillo, Mexico (Invest 98E) is close to tropical depression status as it moves to the northwest at 5 - 10 mph, well offshore from Baja Mexico. This storm is expected to stay out to sea over the next five days. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave 2-day and 5-day odds of development of 90%.

Have a great Labor Day weekend!