Why the decline in tropical waves making it to Florida

[boca]

I noticed over the last few years a marked decline in tropical waves affecting Florida from the E and SE.I guess I can answer my own question that the cause is dry air and SAL. I know when you have an upper ridge of high pressure it causes sinking air which is not condusive for thunderstorm development directly sitting overhead of an area. Why has their been such a decrease in waves over the last few years?

[Vortex]

Boca,

I've noticed the same thing for a number of years. In fact I remember in the 80's/90's it seemed like TW's coming in from the SE in June-Aug were much more common with some events producing 10" of rain...I have thought about this as well for the last several years.

[Frank2]

Likely not to do with this, but, there was a CSU study about 25 years ago (imagine today), that stated the increase in developed (as in covered with cement) land in South Florida was causing a drop in rainfall rates, especially over urban areas - it makes sense, since evapotransporation is less from hard surfaces than from the Earth itself...

I don't think this has to do with what you mentioned, but thought it interesting to note...

Frank

[Kennethb]

The same can be said from here in Louisiana. It seem like it has been years since we had regular easterly tropical waves that created enhance rainfall every week or so during the summer.

The past several years, it has been rather dry. This year has been wetter, but the thunderstorms so far are being enhanced more by westerly troughs.

[weatherwindow]

I noticed over the last few years a marked decline in tropical waves affecting Florida from the E and SE.I guess I can answer my own question that the cause is dry air and SAL. I know when you have an upper ridge of high pressure it causes sinking air which is not condusive for thunderstorm development directly sitting overhead of an area. Why has their been such a decrease in waves over the last few years?

hi steve...just a couple of thoughts...given seafla's lat, say 25-28degN, we would be most affected by stonger, higher amplitude waves...these waves tend to be generated in greater quantity as the itcz migrates further north into sahel region, later in the season...the strength and amplitude of the wave tends to be related to the east to west temp/pressure gradient over the african continent...as the sahel has become hotter, more arid and less savannah-like...the tendency has been for a larger percentage of the waves to move more quickly from east to west and due to drier atmosphere of the now drier sahel, they are less apt to be as "well-developed"...ie higher amplitude and low pressure development along the axis...as they emerge from the african coast..grey, et al(dont have a link)suggested that slower may be more favorable ..in addition, altho i dont think this has much bearing...the greater the percentage of waves generated in any given year which develop into trop cylones, the fewer "higher impact" waves remain to reach our longitude...lately say since 1995, this may have been the case vis-a-vis the 70s and 80s.......rich

[Noah]

AS I have stated before, this is the driest summer ever in my 20 years in Florida. No afternoon storms. Clouds and thunder all over but rain stay about 10 miles east of me. I live about 7 miles from the gulf and we used to get good TS every afternoon for years. This year they are staying inland in my area anyway.
Anyone have reasons for this?

[EDR1222]

Not sure about the tropical waves, but with regard to the thunderstorms...I often here my parents say you could count on a good downpour everyday in summer back years ago. Well, lets say a downpour is a half an inch of rain. If you get that every day, your going to have 15 inches a month during the summer months, which is way above normal if you look at the records through history. That would equal about 45-50 inches of rain...just in the summer time, which is about the yearly average for many areas in Central Florida. I know on the east coast, for the most part we get storms in the summer when the steering flow is out of the southwest, and we do not get that every day in the summer. If the steering currents are weak, or go with the seabreeze it is not going to rain here on the coast very often. The storms form around I-95 and push inland. I would imagine that on the west coast of Florida, it would be the same situation. If the steering flow pushes everything back toward the interior, you are not going to get the storms. I think there are changes from year to year.

[flashflood]

If you get that every day, your going to have 15 inches a month during the summer months, which is way above normal if you look at the records through history. That would equal about 45-50 inches of rain...

Ironically we got about 15+ inches of rain here on the lower south east coast in June. I have not needed to water my lawn since the end of May , this has been a great start to the rainy season for most of us in the Dade and Broward areas.

Most of the rain was from the east coast trough, however we did have a wave that introduced some additional moisture to the area. This week however, we got the dry air and subsidence that has been drying out the most recent waves in the Atlantic. I think this is quite normal for July anyway.

[SouthFloridawx]

I would say that as we continue to move more towards the middle of summer, the ITCZ will lift more northward, and thus we'll be more influenced by tropical waves.

[flwxwatcher]

Hopefully the GFS will pan out as it shows some tropical waves bringing some much needed rainfall to Florida in the longer range period..

[boca]

Another oberservation is that last year we had an abundance of ULL's forming one after the other.This year maybe one a week. I wonder if EL Nino had something to do with all the ULL 's last year.

[windstorm99]

Speaking about things making to florida the lastest CMC developes to be a wave in the ATL in brings into the bahamas.

Pic of the 850mb vort at 144hrs...



More Here

[DESTRUCTION5]

GFS wants to kill your Theory to Boca with mutiple dousings of rain in the 12Z GFS..

http://www.nco.ncep.noaa.gov/pmb/nwprod ... loop.shtml