Explaining May precipitation impacts on hurricane season

[WeatherEmperor]

Hello,

In 2004 I read somewhere(forgot the website) that the precipitation during the month of May in Florida could determine how many hurricanes could threaten the FL east coast. I believe the article mentioned that 2004 had one of the driest May's on record which meant that the Bermuda High was stronger that year which is why Frances and Jeanne hit FL. Im not exactly sure of the details about that. This is what I want to ask you guys about. Is there any validity to that? I did some research for myself about this during the month of May 2004 from the NOAA website. I found drough map graphics for the U.S and take notice in the South East particularly Florida.

May 1:
http://www.cpc.noaa.gov/products/analys ... 1-2004.gif

May 8:
http://www.cpc.noaa.gov/products/analys ... 8-2004.gif

May 15:
http://www.cpc.noaa.gov/products/analys ... 5-2004.gif

May 22:
http://www.cpc.noaa.gov/products/analys ... 2-2004.gif

May 29:
http://www.cpc.noaa.gov/products/analys ... 9-2004.gif

As you can see, Florida received pretty much average precipitation amounts during the month of May 2004. Only during the week of May 22 did extreme southeast FL receive below average precipitation. We all know that the Bermuda High was very very strong during the 2004 hurricane season so why dont these maps indicate that? Can somebody please explain to me if it is true that having below normal precipitation during the month of May in FL is an indicator of the strenght of the Bermuda High? I dont understand. Any help on this would be much appreciated

<RICKY>

[benny]

The Miami Herald had that study a few years ago... it originated from work originally done by the former MIC (Meteorologist-In-Charge) of the Miami Forecast Office, Paul Hebert. He took a look at dry Mays in S Florida, specifically Miami airport I believe, and found some relationship with a dry May foretelling certain major hurricanes in S FL. I think May 1945, 1965, 1992 were exceptionally dry and then major hurricanes came. At least that was the theory. Jim Lushine, the former Warning Coordination Meteorologist (WCM) of the Miami office really popularized the idea. Nothing 100% formal has ever been done on the theory and it hasn't been published.

I don't think anyone really understands why the relationship seems to work in some years and then in others it doesn't. May 2004 was a dry month for S Florida stations in general... however May 2005 ended up being slightly wetter-than-average. There MIGHT be a relationship between the strength of E Coast of the USA high pressure in May (or April/May) that keeps any fronts from the area and provides stronger than average easterlies in the lower/middle atmosphere. any rain is favored on the west coast of florida.. that's where the rainfall idea comes in i think.

There might be some persistence of the mid-latitude ridging over E coast from Apr/May to later in the season.. this is why this whole May rainfall idea has a chance of working. I think I'd rather look at the direct strength of the ridge... but what lat/long boundaries and where is exactly important would require a lot of study for something that is.. a little hand-waving at this point.

[WeatherEmperor]

very interesting. thanx for helping me out benny!

One more thing though. If May 2004 was drier then average for precip in FL, then why don't any of those maps that I posted in above, indicate the below normal precip? Those maps shows that FL received around average precip for the entire month. Also, I noticed that May 2005 was wetter then average for most of FL which could help explain why the Bermuda High was weaker then average in 2005 so perhaps there is some validity to this precipitation thing.

<RICKY>

[weatherwindow]

FWIW...here are the lists of the driest mays, first as measured at the nws/mia office(several historic locations), second, for tri-county sfla, as the sum of the measurments at mia, ft laud, and wpb. list one: driest at miami(from driest to wettest)1965, 1992, 1927, 1952, 1962, 1989, 1935, 1973, 1945, 1903. list two: tri-county sfla 1965, 1935, 1992, 1927, 1945, 1967, 1989, 1903, 1962, 1941...per jim lushine nws/mia(retired) and ncdc...obviously, many hits and misses but the simple hit percentages are 50% in list one and 60% in list two ......rich

[benny]

very interesting. thanx for helping me out benny!

One more thing though. If May 2004 was drier then average for precip in FL, then why don't any of those maps that I posted in above, indicate the below normal precip? Those maps shows that FL received around average precip for the entire month. Also, I noticed that May 2005 was wetter then average for most of FL which could help explain why the Bermuda High was weaker then average in 2005 so perhaps there is some validity to this precipitation thing.

<RICKY>

Those maps have an averaging time period longer than a month. They aren't a cumulative precipitation monitor.. they weight the short-term precip different than the long term (I think Palmer uses at least 6 months of data)

[boca]

If this theory is right we are in for it this year because I think one of the NWS Miami discussion experts talked about this theory I can't remember his name I think it was Lishune.

[benny]

If this theory is right we are in for it this year because I think one of the NWS Miami discussion experts talked about this theory I can't remember his name I think it was Lishune.

Jim Lushine was interviewed for it a while back for the Herald... he retired last year though.

[WeatherEmperor]

I guess Im gonna have to wait a little while longer before I can get a true answer. I just saw a graphic from Apr 22 that shows that cool pocket off the south american coast expanding just a bit. If this a sign that La Nina is kicking off, I cant say that. Just too many variables to speculate on that could impact this season I guess.

<RICKY>

[benny]

I guess Im gonna have to wait a little while longer before I can get a true answer. I just saw a graphic from Apr 22 that shows that cool pocket off the south american coast expanding just a bit. If this a sign that La Nina is kicking off, I cant say that. Just too many variables to speculate on that could impact this season I guess.

<RICKY>

You'll probably have to wait until it forms Seasonal landfall forecasting is in its infancy at best...

[benny]

There should be a landfall probability forecast (enhanced version) this year from Dr. Gray. That will probably be interesting if nothing else.. he uses a different method than the others (Mark Saunders, James Elsner etc)

[WeatherEmperor]

There should be a landfall probability forecast (enhanced version) this year from Dr. Gray. That will probably be interesting if nothing else.. he uses a different method than the others (Mark Saunders, James Elsner etc)

Is he really gonna be doing landfall probability? I thought he was gonna try this winds steering direction thing. What am I missing?

<RICKY>

[benny]

There should be a landfall probability forecast (enhanced version) this year from Dr. Gray. That will probably be interesting if nothing else.. he uses a different method than the others (Mark Saunders, James Elsner etc)

Is he really gonna be doing landfall probability? I thought he was gonna try this winds steering direction thing. What am I missing?

<RICKY>

I think it will be both. He might do one with a prefered area. Or perhaps how many hurricane landfalls in the east coast or gulf coast.. dunno