|Above: Potential Tropical Cyclone 10 off the coast of Georgia and South Carolina, as seen by the GOES-16 satellite at 9 am EDT Monday, August 28, 2017. Image credit: NOAA/RAMMB. GOES-16 data are considered preliminary and non-operational|
A Tropical Storm Watch is posted for portions of the coasts of South Carolina and North Carolina, thanks to the increasing development of an area of low pressure (formerly called 92L) located about 100 miles south-southwest of Charleston, South Carolina at 11 am EDT Monday. This system was designated Potential Tropical Cyclone Ten (PTC 10) by NHC on Sunday afternoon. Satellite images on Monday morning showed that PTC 10 had a modest amount of heavy thunderstorm activity that was gradually increasing in intensity and becoming more organized, but high wind shear of 30 - 40 knots was hindering development. The system was headed north-northeast at 9 mph on Monday morning, on a track that will take it very close to the Southeast U.S. coast on Monday and Tuesday. PTC 10 will bring heavy rains of 3 - 6” and rough surf to the coast of South Carolina on Monday, and to North Carolina and Virginia by Tuesday. The best chances for development into a tropical or subtropical depression or storm may come on Monday afternoon, when wind shear is expected at its lowest value this week, near 30 knots, according to the 12Z Monday run of the SHIPS model. In its tropical weather outlook issued at 8 am EDT Monday, the National Hurricane Center gave PTC Ten 2-day and 5-day odds of development of 90%. The storm is unlikely to gain sustained winds any higher than 45 mph as a tropical or subtropical cyclone, and will merge with a cold front and move to the northeast, out to sea, on Wednesday. An Air Force hurricane hunter plane will investigate PTC Ten on Monday afternoon.
|Figure 1. Projected 5-day rainfall from PTC 10 for the period Monday, August 28 – Friday, September 1, 2017. Image credit: NHC.|
African tropical wave 93L expected to develop
A tropical wave that emerged from the coast of Africa on Sunday night was designated 93L by NHC on Monday morning. Satellite images on Monday morning showed that 93L had a modest amount of heavy thunderstorm activity that was growing in organization, with plenty of spin apparent in the cloud pattern. Wind shear was high, 20 – 30 knots, but was expected to fall to the low to moderate range, 5 – 15 knots, on Tuesday through Friday, according to the 12Z Monday run of the SHIPS model. This should allow the wave to develop into a tropical depression by Friday over the central tropical Atlantic, as predicted by the 0Z Monday runs of our top three models for predicting tropical cyclone genesis--the European, GFS, and UKMET models. These models have been persistent in developing the new system over multiple runs, giving increased confidence that we will see a new tropical depression in the Atlantic by late this week. The wave is predicted to head west to west-northwest at 15 – 20 mph, reaching the northern Lesser Antilles Islands no earlier than Tuesday, September 5. However, the storm will probably gain enough latitude this week to allow it to feel the steering influence of a trough of low pressure passing to its north, resulting in a track that would miss the Lesser Antilles Islands. Only about 10% of the 70 members of the 0Z Monday GFS and European model ensemble forecasts showed the wave affecting the Lesser Antilles next week. However, it is too early to put much confidence in the system’s long-range track until it consolidates into a tropical depression. In its tropical weather outlook issued at 8 am EDT Monday, the National Hurricane Center gave this new wave 2-day and 5-day odds of development of 30% and 70%, respectively.
Mexico’s Baja Peninsula at risk from 94E
An area of low pressure located in the Eastern Pacific several hundred miles south of the southern tip of Mexico's Baja Peninsula (Invest 94E) is producing a widespread area of disorganized showers and thunderstorms, as seen on satellite images. Wind shear was high on Monday morning, at 20 – 30 knots, but is expected to fall to the low to moderate range, 5 – 15 knots, Tuesday through Friday, according to the 12Z Monday run of the SHIPS model. This should allow 94E to organize into a tropical depression over the warm 29.5°C (83°F) waters of the Eastern Pacific later this week. Our top three models for predicting tropical cyclone genesis--the European, GFS, and UKMET models—all developed 94E in their 0Z Monday runs, and predicted a north-northwesterly track that would take the storm close to the southern tip of the Baja Peninsula on Thursday. In their 8 am EDT Tropical Weather Outlook, NHC gave 94E 2-day and 5-day odds of development of 50% and 80%, respectively.