Tropical wave 99L has a chance to develop in the Atlantic
After a period of inactivity in the Atlantic, there is a central Atlantic tropical wave that has a chance to develop. This tropical disturbance is classified as Invest 99L. The system is situated roughly 900 miles southwest of the Cape Verde Islands. The system is moving westward between 10 and 15 mph. Recent satellite image reveals that 99L remains disorganized and scatterometer data suggests that the system does not have a well-defined surface circulation yet. The system also appears to be still attached to an Intertropical Convergence Zone (ITCZ). Additionally, 99L is located at 9°N, which is relatively close to the equator. This latitude does not have sufficient atmospheric spin. Without enough atmospheric spin, the tropical disturbance would struggle to become a tropical cyclone. 99L appears that it would develop slowly as it would remain in relatively favorable conditions with warm sea surface temperatures at 28°C, light wind shear at 10 knots, and fairly moist environment. Saharan Air Layer (SAL) analysis depicts that the SAL is situated north of the system.
Figure 1. Infrared satellite imagery of Invest 99L. Image credit: RAMMB imagery Colorado State University (CSU).
Forecast for 99L
The development of 99L is expected to be gradual. Once the system gains latitude and detaches from the ITCZ, it will likely have a better chance for further development. The SHIPS model forecasts conditions to remain favorable over the next five days. Sea surface temperatures are anticipated to remain warm at about 28°C, which is above the 26.5°C threshold of what a tropical disturbance is needed to become a tropical cyclone. Wind shear is expected to be low. Atmospheric conditions are predicted to remain somewhat moist. These conditions would support further development of 99L in the next several days.
99L is forecasted to remain in a general westward path and later turn west-northwestward aiming at the Lesser Antilles by a high pressure ridge over the Atlantic. Models are spreading out the future path of 99L. Some models forecast the system to enter into the Caribbean Sea and dissipate, while other models predict that the disturbance will move northwestward in favorable conditions and stay north of the Caribbean Islands. How strong 99L can get determines whether or not it moves westward or more northward. If 99L becomes stronger, then it will likely move northwestward. However, if the system remains fairly weak, then it will likely move westward or west-northwestward. I think 99L is forecasted to move west-northwestward and hit the Lesser Antilles. I’m not really confident yet for where 99L will go after it is near the Lesser Antilles. Regardless of development, the disturbance is expected to bring heavy rains and possibly gusty winds to the Lesser Antilles and other Caribbean Islands by the next several days. Interests along the Lesser Antilles and the northeastern Caribbean Islands should monitor the system closely during the next several days. I give 99L a 20% chance of becoming a tropical cyclone in the next two days.
We are now near the active period of hurricane season. If you don’t have hurricane preparedness kit yet, now it is the good time to get it.
In the central Pacific, there is a tropical disturbance producing disorganized showers and thunderstorms on satellite imagery. The system is classified as Invest 90C. The disturbance is situated roughly 450 miles south-southeast of Hilo, Hawaii. 90C is moving westward at about 15 mph. Environmental conditions are not anticipated to be favorable for further development of the system. I give 90C a near 0% chance of becoming a tropical cyclone in the next 48 hours.
Elsewhere, no tropical cyclone development is anticipated in the next two days.
This will likely be my second to the last entry of the year. My next special entry will be released on September 11. I will remind you on that day if anyone forgets. The next entry will be my last update for a while.