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September 2018 Discussions & Observations Thread


Rtd208

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8 minutes ago, LurkerBoy said:

Dang! Was hoping the cane would throw a wrench into the pattern. 

Nope, the tropics blew its load all in one shot and looks to be quiet through at least the end of September. Whatever is left of the circulation from Florence dissipates on the Euro somewhere near Bermuda in about 7 days. On the GFS, it hangs around as a weak low for about the next 300hrs until finally dissipating near Florida. I think the ship has sailed in terms of regeneration, but I supposed stranger things have happened. 

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3 hours ago, bluewave said:

Picked up .70 here in SW Suffolk with the heavy downpours so far.

It was an astonishing 77/77/100% around noon, I wonder if the dew point has ever been this high this late in the year before?

https://classic.wunderground.com/history/daily/us/ny/new-york-jfk/KJFK/date/2018-9-18

Now it feels better, it's gotten less humid and the temps have dropped from a high of 80 to the low 70s  since the winds switched to the north but it's still raining pretty hard.

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1 minute ago, winterwx21 said:

Actually the models are showing another warmup for us around then. Looks as if we could get back to 80 by next thursday-friday (27th-28th).

Oh that sucks, oh well at least the 90s are done and with the shorter days 80 doesn't feel so bad lol.

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17 minutes ago, bluewave said:

The MJO is moving into the favorable phases for more Atlantic tropical development just in time for October. 

ECMF_phase_51m_small.gif.96f83fbe40d80b79f51fc85234e93a08.gif

 

This is interesting because usually in El Nino's seasons usually end early and this one actually seems to be getting busier later in the season.

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Clash of the seasons coming up over the next week to 10 days. An early fall trough arrives over the Midwest with the WAR still hanging on near the East Coast. Strong late September Great Lakes  cutter pattern along the temperature gradient to our west.

gfs-ens_T2maMean_us_1.thumb.png.04aa183ebe27cad5eb302d09065b664c.png

gfs-ens_T2maMean_us_6.thumb.png.c5baf82336523a7c3443f54f7da02ea5.png

 

 

 

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During the September 1-18 period, the temperature averaged 73.3° in New York City. That makes 2018 the 19th warmest case for the first 18 days of September. Based on both the historical data and the latest guidance, the probability that 2018 will see the fourth consecutive September with a monthly mean temperature of 70° or above has increased.

Since 1869, there were 20 prior cases where the temperature averaged 73° or above during the first 18 days of September. In 16/20 or 80% of those cases, the monthly temperature averaged 70.0° or above. In all other cases, just 14% of years saw September average 70.0° or above.

Cases with a 9/1-18 Average Temperature of 73° or above:
Mean September 19-30 temperature: 66.1° (lowest: 57.5°, 1947; highest: 70.2°, 2005)
Mean September temperature: 71.3° (lowest: 68.6°, 1947; highest: 74.5°, 2015)

Cases with a 9/1-18 Average Temperature below 73°:
Mean September 19-30 temperature: 64.5° (lowest: 55.6°, 1871; highest: 74.7°, 1881
Mean September temperature: 67.4° (lowest: 60.9°, 1871; highest: 73.3°, 1881)

For those who are interested, September 1-18, 1881 had a mean temperature of 72.4°, which was the 30th warmest first 18 days of the month.

In terms of the guidance (using the first 18 days of September and the MEX MOS and EPS), the estimated mean temperature for September 2018 fell within a 70.5°-72.5° range. The implied probability of September’s having a mean temperature of 70.0° or above was 75%. In the coldest scenario, the implied probability was 64%.

Such a warm September is consistent with the long-term observed warming that has seen the return time for September cases with 70.0° or warmer average temperatures shorten.

Return Times for September Cases with Average Temperatures of 70.0° or Above (1869-2017):

Before 1980: 5.0 years
1980-2017: 3.2 years
2000-2017: 2.3 years
2010-2017: 1.6 years

1869-2017 Period: 4.4 years

Yesterday’s 1.19” rainfall brought New York City’s year-to-date precipitation to 44.90”. That ranks as the 71st highest on record in New York City. Based on this data and both the historic (1869-2017) and recent (1971-2017) periods, 2018 will very likely see 50.00” or more precipitation. 60.00” is possible. The lowest 9/20-12/31 precipitation on record is 5.68”, which occurred in 1998. Even that figure would bring the 2018 total above 50.00”.

1869-2017 Data:

Implied probability of 50.00” or more: 96%
Implied probability of 60.00” or more: 24%
Mean 9/20-12/31 Precipitation: 12.21”
Mean Annual Precipitation: 45.27”

1971-2017 Data:

Implied probability of 50.00” or more: 96%
Implied probability of 60.00” or more: 42%
Mean 9/20-12/31 Precipitation: 14.12”
Mean Annual Precipitation: 50.42”

Since 1970, in conjunction with the observed warming, the climate has also grown wetter. Extreme wet outcomes have grown more common.

This trend can be seen throughout the Northeast. Indeed, a disproportionate share of the 20 wettest years has occurred since 1970. Select data follows with the start of the climate record in parentheses:

Albany (1874): 80% of the 20 wettest cases
Bangor (1925): 60% of the 20 wettest cases
Boston (1872): 40% of the 20 wettest cases
Burlington (1884): 35% of the 20 wettest cases
Caribou (1939): 90% of the 20 wettest cases
Concord (1868): 35% of the 20 wettest cases
Hartford (1905): 75% of the 20 wettest cases
New York City (1869): 80% of the 20 wettest cases
Newark (1931): 75% of the 20 wettest cases
Philadelphia (1872): 50% of the 20 wettest cases
Portland (1871): 70% of the 20 wettest cases
Providence (1904): 65% of the 20 wettest cases
Worcester (1892): 60% of the 20 wettest cases

The following locations have seen at least 25% of their 20 wettest years occur 2000 or later: Albany, Burlington, Caribou, Concord, Hartford, New York City, Newark, Portland, and Providence.

For New York City, the 20th highest annual figure is 53.79”. Based on the 1869-2017 data, the implied probability that 2018 will surpass that amount is 79%. Based on the wetter 1971-2017 period, the implied probability is 85%.

Farther south, Baltimore has already registered its 17th highest annual precipitation amount. There remains a possibility that Baltimore will reach or exceed its record figure by year’s end. Wilmington, NC, which has already received 86.40” precipitation, boosted by Hurricane Florence, has eclipsed its old mark. In fact, that figure is among the highest on record in North Carolina. Only a few locations in North Carolina, including the following have seen higher amounts of precipitation in a year:

Boone: 112.14”, 2013
Blowing Rock: 93.32”, 1992
Cape Hatteras: 90.84”, 1989
Coweeta Experimental Station (near Otto, NC): 93.92”, 2013
Grandfather Mountain: 89.12”, 1979
Highlands: 111.57”, 2013;
Morehead City (2 WNW): 91.51”, 2003
New Bern (3 NW): 89.45”, 1908
Rosman: 126.73”, 1961
Southport (5 N): 89.79”, 1999
Tryon: 92.76”, 1979

Cape Hatteras, Morehead City (2 WNW), New Bern (3 NW), and Southport (5N), all of those locations are in the vicinity of the Appalachian Mountains.

 

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