Wednesday 8 a.m.
A high pressure area drifting east from the Great Lakes is providing the entire Northeast a stunningly bright and sunny late August day. The humidity will be moderate. In sharp contrast, Isaac is continuing its painfully slow sojourn along the Gulf Coast. The storm is weaker than Katrina, but it is moving much more slowly. This means the teeming torrents of rain, the hurricane-force wind gusts and the flooding (from various causes) are dragged out over a long period of time. As of 8 a.m. EDT, nearly a half million people in and around New Orleans were without power. This video shows more, and includes a discussion about where Isaac's moisture will eventually go. Until we see otherwise, we should assume that Isaac will continue to cause heavy rain long after its winds drop below tropical storm stage levels.
This picture taken around 7 a.m. EDT is a spectacular display of Isaac. Until we see otherwise, we should assume that Isaac will continue to cause heavy rain long after its winds drop below tropical storm strength.
...after all that, the point is that zone will be north of most of the eastern half of the country. It will be very warm to hot south of the jet stream. However, weakening cold fronts can advance south of the jet stream. then return north as the next disturbance in the flow approaches.
Yesterday, the temperature hit 92 at Newark, New Jersey, and 90 in Boston. The following map shows a northerly flow affecting the Northeast today, and so it will be noticeably cooler and less humid.
This map shows lightning strokes from 8 a.m. ET yesterday through 7:54 a.m. ET today. There was quite a bit of it in Utah, Colorado, New Mexico and Arizona. For the whole map, 156,172 lightning strokes were recorded.
Looking at the west-to-east upper air flow over New England well ahead of the storm, it seems like the hurricane should stay out at sea, However, as we look through the series of maps, we see the upper-air flow congealing into a strong eastern trough that helped the storm to come right up the coast instead of heading out to sea.
On this satellite picture, we can see the basically dry weather in the Eastern states. The cold front that will ease the midweek heat in the Northeast is shown by the band of thunderstorms in the Midwest. The thunderstorms may weaken and become more scattered as the front comes into the Northeast.
A storm in the tropical Atlantic is being observed for possible strengthening. This map shows the variety of models purporting to show where the center will go. Most solutions suggest it stays well offshore, but you will notice a few outliers suggesting more threat.