Tropical Storm Harvey has continued to dump torrential rainfall over Southeastern Texas today, causing catastrophic flooding. The flooding is expected to continue for several days as Harvey moves very slowly, possibly re-emerging into the extreme northwestern Gulf of Mexico. Aside from Harvey, the National Hurricane Center (NHC) has initiated advisories on Potential Tropical Cyclone Ten, which is expected to develop into a tropical cyclone on Monday before it eventually merges with a cold front. There is also a tropical wave currently located over western Africa that has a potential to develop into a tropical cyclone over the eastern tropical Atlantic by the end of this week.

Harvey likely to change little in intensity as it floods Southeastern Texas, could barely reemerge over water

As of 10:00 p.m. CDT (11:00 p.m. EDT), Tropical Storm Harvey was centered near 28.8°N 96.6°W, and was moving east-southeastward at about 3 mph. Maximum sustained winds were 35 knots (40 mph), with an estimated minimum pressure of 1000 mb. Harvey has changed little in organization today, although tropical storm force winds have not been reported during the past few hours. Harvey is expected to reemerge into the Gulf of Mexico by tomorrow evening. After that time, some slight restrengthening is possible, but significant strengthening appears unlikely due to Harvey’s lack of an inner core and its proximity to land. Even though Harvey is not likely to strengthen much over water, catastrophic flooding is likely to continue over Southeastern Texas for the next several days. Harvey is likely to make a second landfall on Wednesday farther east in Texas, not far from the Louisiana border. A Tropical Storm Warning is currently in effect from Mesquite Bay to High Island. Harvey is then expected to accelerate northeastward and could retain its status as a tropical cyclone for five days or perhaps even longer.

It should be stressed that the main threat with Harvey is heavy rain and flooding. Rainfall amounts of 15-25 inches are likely, with isolated amounts of up to 50 inches not out of the question. This much rainfall can cause catastrophic flooding. Do not attempt to travel in these flooded conditions if you are in a safe place!

Potential Tropical Cyclone Ten expected to develop off coast of Southeastern United States, but will likely remain weak due to strong shear

As of 11:00 p.m. EDT, Potential Tropical Cyclone Ten was centered near 30.5°N 80.8°W, and was nearly stationary. Maximum sustained winds were 30 knots (35 mph), with an estimated minimum pressure of 1007 mb. An ASCAT pass from earlier today indicated that Ten was producing winds to near tropical storm force, but the circulation was elongated and not well defined. The National Hurricane Center (NHC) gives Ten a 90 percent chance of development within 48 hours and five days. I think these chances are too high, and I only give PTC Ten a 70 percent chance of development over the next 48 hours since wind shear is expected to remain moderate to strong and the system is expected to merge with a cold front by late Tuesday.

Overall, deep convection has increased with the disturbance today (previously known as Invest 92L), but as noted above, the circulation is not well defined. Wind shear is expected to remain at least 25-30 knots over the next several days, and PTC Ten only has about 36-48 hours to develop into a tropical cyclone. Significant strengthening is unlikely in the short term, but PTC Ten is likely to strengthen into a powerful extratropical cyclone by late this week as it is expected to move out to sea. The official NHC forecast predicts that PTC Ten will become Tropical Storm Irma by tomorrow morning, but I think this could be a little too soon based on the current structure of the disturbance. Residents along the coast of the Carolinas should monitor the progress of this system, as rain totals of 2-4 inches are possible along portions of the coast. A Tropical Storm Watch is currently in effect from South Santee River, South Carolina to Duck, North Carolina, as well as the Albemarle and Pamlico Sounds. An Air Force Reconnaissance Aircraft is scheduled to investigate PTC Ten tomorrow afternoon to see if a well-defined circulation has formed.

New tropical wave has a chance to develop

A tropical wave is currently located near the coast of western Africa, and is producing disorganized showers and thunderstorms. The NHC gives this wave a near zero percent chance of development within 48 hours, and a 40 percent chance of development within five days. Model support for development of this wave is strong – the 12z Sunday ECMWF, CMC, and UKMET model runs, as well as the 18z Sunday GFS model run, all showed development of this wave during the next five days. There is a chance that this wave could rapidly develop as soon as Tuesday or Wednesday, when it will likely be near the Cabo Verde Islands. The rapid development scenario is suggested by the GFS, ECMWF and UKMET models. Conditions are expected to be favorable for gradual development, and this wave could eventually develop into a hurricane by next week. Both the GFS and ECMWF models indicate that it is possible that this wave could develop into a classic long-tracked “Cape Verde hurricane.” Although a quick development would usually indicate a recurve out to sea, global models indicate that this system could take a west-southwest or even southwest dive by next weekend, and that means that the Northern Leeward Islands and even the Eastern United States could still be in play in the long range. However, until a well-defined center of circulation forms, forecasting track and intensity is extremely difficult and uncertain. Assuming Potential Tropical Cyclone Ten becomes Tropical Storm Irma as expected, this system would be named Jose if it becomes a tropical storm. I give this wave a 10 percent chance of development within 48 hours, and a 50 percent chance within five days.

I will be back tomorrow with another post.