The tropics are very active today in both the Atlantic and Eastern Pacific. In the tropical Atlantic, a tropical wave which has just exited the coast of Africa has been designated Potential Tropical Cyclone Six and Tropical Storm Warnings have been issued for parts of the Cabo Verde Islands. This wave should develop into Tropical Storm Florence on Friday, and could become a hurricane as it moves west-northwestward by late this weekend. There is also a tropical wave currently being monitored over the northeastern Caribbean, which has a low chance of becoming a tropical cyclone by early next week over the Gulf of Mexico. The eastern Pacific also remains busy, with Hurricane Norman now a high-end Category 4 hurricane on the Saffir Simpson Hurricane Wind Scale. Hurricane Miriam is also active in the Central Pacific as a Category 1 hurricane, and poses no threat to land.

Potential Tropical Cyclone Six gradually becoming better organized, likely to become a tropical cyclone on Friday

After a very quiet August so far in the tropical Atlantic which has featured no tropical cyclones south of 30°N, it appears as if the tropical Atlantic will squeeze out a tropical cyclone before the month ends. The National Hurricane Center initiated advisories on Potential Tropical Cyclone Six Thursday morning, a tropical wave which exited the coast of Africa earlier today. Advisories were initiated since a Tropical Storm Warning has been issued for the Cabo Verde Islands of Santiago, Fogo and Brava. A broad area of low pressure has developed with the wave, but it still does not possess a well-defined center yet. Once it develops a well-defined center, which it should tonight or early Friday, it will be upgraded to a tropical depression. The National Hurricane Center (NHC) currently gives the system an 80 percent chance of development within 48 hours, and a 90 percent chance within five days.

As of 5:00 p.m. EDT Thursday, Potential Tropical Cyclone Six was located near 12.9°N 19.4°W, and was moving westward at about 9 mph. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1007 mb. POTC Six is expected to remain in a somewhat conducive environment for the next few days, with wind shear light to moderate at less than 20 knots, and a mid-level relative humidity value currently near 70%. This should allow Six to develop into a tropical cyclone soon and possibly attain hurricane strength by Sunday. Although wind shear is unlikely to be strong enough to limit intensification, Six will move over sea surface temperatures of about 26°C from Sunday until early next week as well as a slightly drier environment, which should slow the strengthening rate or perhaps cause the system to weaken slightly. POTC Six probably will not reach its peak intensity until at least a week from now, when it is expected to be over warmer waters in the central subtropical Atlantic. It is highly unlikely that POTC Six will pose any threat to the United States, though the system is expected to bring tropical storm conditions to parts of the Cabo Verde Islands on Friday. All global models develop POTC Six into a tropical cyclone, and it appears to be on its way. The next name on the Atlantic naming list is Florence.

Tropical wave over eastern Caribbean may warrant monitoring over the Gulf of Mexico next week

A tropical wave over the eastern Caribbean Sea is producing disorganized showers and thunderstorms. However, there are no signs of a surface circulation at the moment, and tropical cyclogenesis is not expected during the next few days. After that time, environmental conditions may become a bit more favorable when it reaches the Gulf of Mexico early next week. The National Hurricane Center (NHC) currently gives this system a near zero percent chance of development within 48 hours, and a 10 percent chance within five days. None of the reliable 12z models showed significant development with this disturbance, though the ECMWF model had been showing development in prior runs. This wave will need to be watched in the Gulf of Mexico, since we are nearing the peak of the season.

Norman a Category 4 hurricane over the Eastern Pacific

After a period of explosive intensification last night, Hurricane Norman rapidly intensified into a strong Category 4 hurricane over the eastern Pacific, making it the fifth major hurricane of the very active 2018 Pacific hurricane season. As of 2:00 p.m. PDT (5:00 p.m. EDT) Thursday, Hurricane Norman was centered near 17.5°N 118.8°W, and was moving westward at about 9 mph. Maximum sustained winds were 130 knots (150 mph), with an estimated minimum pressure of 937 mb. Although some slight additional strengthening is possible, Norman is likely near its peak intensity, and a slow weakening trend should begin tomorrow as it begins to move towards cooler waters. Norman poses no imminent threat to land. While most of the model guidance keeps Norman of the Hawaiian Islands, it is still too soon to rule out impacts to the islands.

Miriam no threat

Hurricane Miriam is a Category 1 hurricane over the Central Pacific and poses no threat to any land areas. As of 11:00 a.m. HST (5:00 p.m. EDT) Thursday, Hurricane Miriam was centered near 15.7°N 141.6°W, and was moving north-northwestward at about 8 mph. Maximum sustained winds were 75 knots (85 mph), with an estimated minimum pressure of 982 mb. Some slight additional strengthening is possible with Miriam over the next day or so before the cyclone moves northward towards cooler waters and begins to weaken.

I will be back with an update on the tropics tomorrow.