We now have tropical storms Jose and Katia to throw into the mix of an active weather pattern in the Atlantic and Gulf of Mexico. Our main concern is Irma which is still forecast to move up towards Florida by the end of the week – the GFS has Irma taking a sharp turn to the north as it approaches the keys and then moving up the east coast into Georgia and the Carolina’s – still a bit early to tell for sure as these storms have a mind of their own.
Katia is expected to drift into Mexico. Jose is expected to turn into a hurricane by early tomorrow morning – below are the current graphics from the National Hurricane Center.
Irma is a Cat 5 hurricane and will have devastating effects. Islands under hurricane warning include Aguilla, Antigua, Barbuda, Puerto Rico, the US and British Virgin Islands, Montserrat, St. Kitts and Nevis, Saba, St. Eustatius, St. Martin/St. Maarten, St. Barts, the Dominican Republic from Cabo Engano to the northern border with Haiti, Guadeloupe, the southeastern Bahamas and the Turks and Caicos Islands.
No changes to the previous forecast. Diurnally driven showers and thunderstorms will be the rule today and Thursday in agreement with SPC outlooks. Activity over and near Lake Michigan may be a bit more persistent and is expected to intensify early Thursday morning with the approach of an upper PV max that should grow the marine boundary layer and raise convective instability.
As this PV max rotates around the sharp upper trough Thursday, we expect precipitation and thunderstorm chances to overspread the entire forecast area. The upper trough slowly exits to the east on Friday. There may be residual lake effect precipitation curling into far southwest lower Michigan early in the day, but this shouldn`t last long with increasingly anticyclonic low level flow building into the area with surface high pressure. .
We continue to expect a prolonged period of dry and increasingly mild temperatures through the period. The upper trough that will be plaguing the region through Thu will have moved out by the beginning of the long term on Friday night. This will be replaced by a somewhat flat, yet strong upper ridge that will build over the area.
This ridge will not go far during the period as Hurricane Irma, the departing trough to the east, and another trough to our north will all push to keep the upper ridging in play. Temperatures will initially be rather cool with the residual cool air mass holding over the area initially. A warmer air mass will eventually advect into the area as the sfc ridge slips SE, and a WSW low level flow takes shape.