The Southeast USA Monsoon Climate debate. (hottest, warm, rainfall, Chicago)

[wavehunter007]

There is a big debate going on here at work whether the deep south Atlantic States (Florida, coastal Georgia, southern/coastal South Carolina) are more of a “Subtropical Monsoon climate” (Cw)…rather than the current Koppen classifircation of “Humid Subtropical climate” (Cf). Certainly, if you look at rainfall profiles from South Carolina southward to the Florida Keys…the hot season from May through October has much more rainfall than the cold season (Nov - April)... and July,August, and September in locations like Charleston or Daytona Beach have twice as much rainfall as any of the cold season months.

Here is a short and interesting article about the debate by NOAA climate scientists, at least in terms of northern Florida.

NWS Melbourne Wet-Dry Season

What’s your take…should at least northern Florida be reclassified as Subtropical Monsoon or Subtropical Wet /Dry. Should the Humid subtropical Cf classification remain? What’s your opinion?

[Infamous92]

Very interesting, I checked and they're certainly more monsoonal than Cf areas further north such as the DMV, DE, & Philly/NJ/NYC/LI. They should be classified as such especially considering the Cf climate is very broad.

[MrMarbles]

Interesting. Looks like if there is a monsoon, it is limited to the narrow coastal belt. Inland cities like Atlanta and Charlotte have a much more even precipitation pattern.

[ColdCanadian]

Raleigh NC gets (slightly) more rain in summer than any other season.
Going further east or south from there, the summer rain peak gets more pronounced.

[wavehunter007]

What prompted this debate was actually the North Florida/south Georgia forest fires in 2007. A young woman here at work who lives in St.Augustine, Fl…commented that they (the fires) are worse when the “wet” is slow to arrive. The more we started talking, the more that it seems (to some of us) that the there is a wet/dry or monsoon in the eastern portions of the south Atlantic/eastern Gulf states. I did a little research and it appears that even NOAA is even debating this issue. In a climatological sense…what makes the rainy season confusing in the southeastern USA is that many stations well inland have no accent on seasonal rainfall. This is a bit weird, because most subtropical regions located on a large landmass…well inland…show at least some accent on warm season rainfall (inland southeast China, inland Queensland…etc). This is not the case in cities like Atlanta, Dallas,..etc…rainfall is even throughout the year.

As you move toward the southeastern portion of the region (from around New Orleans east to lower South Carolina, then south to Florida)…a high sun rainfall situation develops typical of humid subtropical climates (Cfa). Cities like Savannah, Charleston, Jacksonville, New Orleans, etc seem to have a strong flow off the ocean in the hot season with twice the rainfall as the cold season. Looking at a normal summer weather map this would make sense because there is a deep current of humid tropical air aloft over the region. I checked monthly rainfall at a few NWS stations, If you look rainfall in the 4 hottest months …vs the 4 coolest months …the monsoonal pattern becomes apparent the further south you get:

Savannah rainfall
June/July/Aug/Sept –23.84 inches.
Dec/Jan/Feb/Mar –13.31

Jacksonville rainfall
June/July/Aug/Sept – 25.10
De/Jan/Feb/Mar – 13.24

Orlando rainfall
Jun/July/Aug/Sept – 26.87
Dec/Jan/Feb/Mar – 10.66

Miami rainfall
June/July/Aug/Sept – 31.35
Dec/Jan/Feb/Mar – 8.69

It interesting that not only does hot season rainfall increase as you move southward…but the ratio of warm to cold season rainfall increase: In Savannah, the hot season has slightly less than twice as much as the cold season…by the time you get to Miami…the hot season has three and half times much rainfall as the cold season! I guess the other side of that is that winters get drier the further south you go from Savannah to Key West. So it seems while the inland southeast is quite odd for its geographic location…the deep coastal southeast and Florida are more typical of humid subtropical climates…in that rainfall follows the sun. As NOAA above points out, the pattern of seasonal rainfall once you get into north Florida is so strong…that subtropical monsoon Cw seems the appropriate climate classification.

[nei]

Probably for different reasons, some places in the Midwest are much wetter in the summer than winter. I assume this is normal for places away from bodies of water, so they do not deserve a Cw/Dw designation, but the contrast is as large as Florida. For example:

Minneapolis Precipitation

June/July/Aug/Sept - 15.12
Dec/Jan/Feb/Mar - 4.69

Chicago Precipitation

June/July/Aug/Sept - 15.34
Dec/Jan/Feb/Mar - 9.32

In contrast:

New York City Precipation

June/July/Aug/Sept - 16.91
Dec/Jan/Feb/Mar - 15.6

Portland, Me Precipitation

June/July/Aug/Sept - 13.02
Dec/Jan/Feb/Mar - 15.61

[Infamous92]

I was just Wikipedia'ing Nassau (Bahamas) for something else and saw it has a Tropical Monsoon Climate, now I assume it's climate can't be that much different than South Florida's so the coastal SE US must be very close to CW status.

[ColdCanadian]

Originally Posted by wavehunter007

It interesting that not only does hot season rainfall increase as you move southward…but the ratio of warm to cold season rainfall increase: In Savannah, the hot season has slightly less than twice as much as the cold season…by the time you get to Miami…the hot season has three and half times much rainfall as the cold season!

In places like Savannah, they probably don't need all the winter rain with their cooler temps.
Usually they appear fairly green in winter, for the plants that aren't dormant.

Central and South Florida from my experience usually looks a bit "scorched" from lack of rain.
Unwatered grass in central FL is often "crispy" in winter; actually hurts to walk on barefoot.

[wavehunter007]

Originally Posted by nei

Probably for different reasons, some places in the Midwest are much wetter in the summer than winter. I assume this is normal for places away from bodies of water, so they do not deserve a Cw/Dw designation, but the contrast is as large as Florida. For example:

Minneapolis Precipitation

June/July/Aug/Sept - 15.12
Dec/Jan/Feb/Mar - 4.69

Chicago Precipitation

June/July/Aug/Sept - 15.34
Dec/Jan/Feb/Mar - 9.32

In contrast:

New York City Precipation

June/July/Aug/Sept - 16.91
Dec/Jan/Feb/Mar - 15.6

Portland, Me Precipitation

June/July/Aug/Sept - 13.02
Dec/Jan/Feb/Mar - 15.61

I knew that places west of the Ohio Valley were drier in winter…but I didn’t think the difference was that large. Wow, in MN the numbers look a lot like a winter monsoon to me – lol.

The East Coast above North Carolina numbers doesn’t surprise me. Precip is fairly balanced throughout the year (although in some years summers are quite wet from NYC/NJ/CT area south). In fact, I think that many stations from Massachusetts northward actually have more precip in the cold season than in the warm season (of course the summers are far from dry)...and that shows in the numbers for Portland.

[texdav]

Alot of sates had very wet winters which allowed them to get out of severe droughts last few years in summer. So far this year we are short of rain but never get like some do being on the coast.