Thursday, August 12, 2021

Tropical Depression Fred: 11 August, Update A

Well that was a rather nice little break, wasn't it? Plenty of time for tea and a slice o'cake, but now I am slightly late to the Flintstones viewing party. 

Tropical Depression Fred, as he's currently known, was a blob quietly chugging across the Atlantic and into the Caribbean until yesterday evening (Tues., 10th), when he gained enough steam to be named a Tropical Storm just south of Puerto Rico. He's not really been very strong though, reaching maximum winds of 45mph just before making landfall in the Dominican Republic at around 2pm local time as a Tropical Storm. I suppose some of Fred is now a page right out of history. ;-) 

He is currently at 19.5N, 72.2W, over Haiti, heading WNW at 15mph:

He will emerge from Haiti by the morning (Thurs.) and the forecast track keeps him over water and as a Tropical Depression until Friday. He is currently fairly weak with winds of 35mph, central pressure of 1009mb. 

The Tropical Depression status at the moment because he is moving over hilly land but also because there is some wind shear, which we can see in the satellite imagery because it looks like the convection (rain) is to the south and east of the center: 

It is a little difficult to see the center at the moment though because he isn't very well developed - but the NHC think it is over northern Haiti, even though the convection makes it appear as though it is to the south. 

The real clue that he is experiencing wind shear is in the vorticity (circulation) maps (remember those from this <Technical Alert!> just over a month ago?). He does have good circulation in the lower half of the troposphere, but the lower level is west of the mid-level, which means he is slanting vertically. To see this, here is the map from the lowest level (850mb):

Found Fred? (the red blob over Haiti). Here's the mid-troposphere map at 500mb: 

In this map the red blob is to the east compared to the lower level which shows he is experiencing wind shear. For a well formed storm, the red blobs would line up. Easy peasy, right? :-) 

It looks like the wind shear will continue as he moves over water tomorrow, but that water is a bit toasty - the surface is warmer than 28 deg C and the upper ~75m of the water is warmer than 26 deg C, which is what a storm needs to keep it going. So there is a chance of strengthening, but the closer he stays to Cuba, the weaker he will remain - it really depends on his exact path in that Cone of Uncertainty. 

I'll be back tomorrow....

Ciao for now,




These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and local weather service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know. 

No comments: