The Remnants Of Tropical Storm Alberto Could Bring A Flash Flood Threat. Discussing Rain Totals...
This has been an interesting May thus far. We are on pace to break the record for the "warmest May" on record and it is not even close. The by product of this warm May has been spotty t-storms that have either brought you a lot of rain or next to nothing. We have seen large ranges in the rain totals, but some very clearly still need some rain. You can see the lack of rain in areas as many lawns and farms are already looking stressed. Alberto will give us an opportunity for some solid rain in areas, but I am not convinced we all get the soaking rain. We also know tropical systems can bring too much rain and times and a flash flood threat is real for some with this storm. Let's jump in and look at potential rain totals.
Tropical Storm Alberto Is Approaching...
Tropical systems are well know for producing sizable rain totals near the center, but not always everywhere. That means it becomes critically important to note where this low is going, so we can assess heavy rain potential. Alberto has made landfall in Florida and it is making it's move to the north as we speak. Notice the swirl of the clouds near the Gulf of Mexico with the bands spread out as far as southern KY.
Alberto is forecast to make a move to the north and through western KY. The consistency within the data is high lending a lot of credibility to the track of this storm. This is called a "spaghetti plot" showing all the various computer models we use to forecast. Notice how tightly clustered they are on the track through western KY.
No surprise on the NHC track showing Alberto moving northward then across our western counties late Tuesday into early Wednesday. You can see the sustained winds are not impressive at all as it approaches, so the concern for widespread strong winds are low.
How Much Rain Does The Data Indicate?
This is a setup where there clearly will be "tropical downpours" since this is a sub-tropical storm. The storm will weaken by the time it arrives, so the tropical storm force sustained winds will not be a concern. Looking through the data, we can see quite a range still. It is critically important to note that with tropical downpours, there can be a large variations in rain totals from one location to the next. What we do see is consistently more rain along the track of the low and that likely means the heaviest rain could fall west of I-65. As you look through the data, note the name of the computer model and the time period on the top right of each image. The NAM only goes out 84 hours, so it stops late Thursday while the GFS and EURO go through Friday.
The WPC (branch of the NWS) is forecasting some very solid rainfall for our area through Friday. You can see they also bias the heaviest close to the track of the low in western KY / IN, but show 1" - 2" near and east of I-65. Closer to the low, they are forecasting 2" - 3.5" west of I-65 with the higher totals from Madisonville, KY to Evansville, IN.
My Thoughts On Rain Timing & Totals
With the remnants of Alberto moving across our area on Tuesday and Wednesday, the NWS has issued a Flash Flood Watch for much of the area that goes into effect late Tuesday. This watch does include the Louisville area.
Tuesday does not look like an all day rain. The rain chance should increase late on Tuesday with the best chance on Tuesday night. With tropical systems, we traditionally see the heaviest rain near the low which travels through western KY. I think the greatest chance of more widespread heavy rain therefore falls along and west of I-65. That said, there is a lot of moisture with this system and even your general storms can produce extremely heavy rain within a setup like this. The window for the heaviest is late Tuesday and Wednesday, but scattered storms remain on the table for Thursday.
I think this is a good candidate for 1" to 3" of rain for our area. I think the areas that would be on the lower edge are likely east of I-65, but there will be some locations along and west of I-65 that could exceed 4" or 5" of rain. I think the greatest potential for the heaviest rain will be west of I-65 and closer to Owensboro and Evansville. Since these waves will be convective (t-storms) in nature, we can see wide ranges for the areas that get caught under repeated t-storms. The heavy rain potential is something I will be watching closely.
It is also worth noting that the right side of tropical systems can and do produce short lived, quick tornadoes at times. We are in the right side of Alberto, so I cannot rule out a couple quick tornado warnings late Tuesday or Tuesday night. The threat is not large, but there is definitely a chance of a couple of warnings.
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