Steamy Monday: Gully washers north, metro storm chances

Another day, another Minnesota severe storm and heavy rainfall event.

Slow moving thunderstorms produced four preliminary tornado reports and dumped more multi-inch rainfall totals across northern and central Minnesota this morning.

The latest deluge formed as two storm clusters across northern Minnesota and merged into line of storms with torrential rains feeding off the high dew point air mass to the south.

Rainfall totals of 2 to 4 inches promoted flash flood warnings near Alexandria, Minn., this morning. Heavy rainfall totals run east across Minnesota to Aitkin and the Lake Mille Lacs area.

Weakening trend

The trend on the morning storms is for them to weaken as they outrun their support system north of the metro. Then we watch for potential redevelopment this afternoon and evening.

Twin Cities metro: 'heavy rainers' this evening?

Pinpointing the precise location of torrential and potentially flash flood producing rainfall events several hours in advance is still close to a meteorological impossibility. That said, there is the potential for more multi-inch gully washers this afternoon and evening across southern Minnesota, and maybe in the metro.

The National Oceanic and Atmospheric Administration's North American Mesoscale Forecast System 4 km model suggests localized blow-ups that could dump another 2-plus inches in a hurry close to the the metro this evening. It could be an interesting evening commute in some parts of the Twin Cities.

Slow moving front

The heavy rain zone is being triggered by a slow moving cold front crawling across Minnesota today. The front is capable of triggering another wave of slow-moving heavy rain clusters this afternoon and evening across southern Minnesota. A much drier air mass pushes in starting tomorrow that could produce a welcome dry spell through Friday.

The Twin Cities National Weather Service office does a nice job of laying out the three different weather patterns this week. Stormy Monday leads to a pleasantly dry week, then probably an unsettled Labor Day weekend. Here's the CliffsNotes version of the forecast this week.

Wet Labor Day weekend?

Right now next weekend looks unsettled. There's still the potential for another 90-degree day as we move into September.

Tropical Trouble: Active storms may affect U.S. this week

Not one but two tropical systems have the potential to affect the United States this week. While Hurricane Gaston spins harmlessly in the open Atlantic, two other systems may interact with the U.S. this week.

Here's the Atlantic basin overview from NOAA's National Hurricane Center.

Tropical Depression Eight brushes North Carolina's Outer Banks Tuesday, possibly as Tropical Storm Hermine.

Of potentially greater interest and impact, Tropical depression Nine in the Gulf of Mexico. This long watched pot may finally boil over and reach near hurricane strength this week, and probably curve northeast into northern Florida north of Tampa. Hello Tropical Storm Ian?

Model spread

They call them "spaghetti models" for good reason. There is still a fair amount of model spread in the eventual path of TD 9, but solutions appear to be converging on a north Florida landfall in the next 72 hours.

Primary threat: Heavy rainfall

The primary threat for these systems remains heavy rainfall, especially in Florida. I could easily see some 10 inches-plus rainfall totals around Tampa and Fort Myers in the next week before all is said and done.

The Gulf of Mexico is warm, with water temperature in the upper 80s. Unexpected rapid intensification is possible. As we say in the weather biz, stay tuned.