There are currently no active tropical cyclones in the Atlantic or eastern Pacific basins, but there is a low pressure system that may develop in each basin. In the Atlantic, a non-tropical low (Invest 98L) is developing a new center of circulation and could gradually acquire subtropical characteristics by early Thursday. In the eastern Pacific, a well-defined low pressure system (Invest 97E) is likely to develop into a tropical depression over the next day or two as it tracks westward towards the central Pacific. Neither system poses an imminent threat to land.

As of 18:00 UTC Tuesday, Invest 98L was centered near 36.3°N 46.9°W, and was moving northeastward. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1013 mb. The National Hurricane Center (NHC) gives 98L a 40 percent chance of development, both within 48 hours and five days. Shower and thunderstorm activity has increased to the east of the developing circulation center, and 98L could acquire subtropical or tropical characteristics (most likely subtropical) tomorrow. The GFS, ECMWF and UKMET models are in good agreement that 98L will develop a more defined center by Wednesday morning. Strong wind shear has been keeping 98L poorly organized over the last few days, but based on the SHIPS model, the shear is expected to decrease to less than 15 knots in about 24 hours. 98L is currently located over marginal sea surface temperatures near 27°C (80.6°F), and in a marginally moist environment. The next name on the Atlantic naming list is Ernesto. If Ernesto develops into a subtropical cyclone, it will be the fourth system of the 2018 season to have subtropical characteristics at some point (and the one storm to be tropical during its entire lifespan – Chris – formed from non-tropical sources). This reinforces the idea that 2018 will likely be a season with more developments of non-tropical origin, as dry, sinking air is currently keeping the deep Atlantic tropics quiet.

As of 18:00 UTC Tuesday, Invest 97E was centered near 11.1°N 119.2°W, and was moving westward at about 10-15 mph. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1009 mb. The NHC gives 97E an 80 percent chance of development within 48 hours, and a 90 percent chance within five days. 97E has now developed a well-defined circulation, though moderate easterly wind shear currently is keeping the circulation exposed to view. 97E should become a tropical depression by Thursday, possibly as soon as tonight. The 12z Tuesday ECMWF and UKMET models develop 97E into a weak tropical cyclone, but the 12z GFS does not. 97E is likely to take a similar track to Hurricane Hector, but will probably be weaker. The environment for 97E appears conducive for development, with wind shear expected to be less than 10 knots for the next five days, along with sea surface temperatures above 27°C (80.6°F) and mid-level relative humidity values over 60 percent. Although global models only develop 97E slightly, it would not be surprising to see 97E become a hurricane with the environment forecast by the SHIPS guidance. The next name on the eastern Pacific naming list is Lane.

I will be back with another post on 98L and 97E tomorrow.