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September 2020 wx discussion


forkyfork

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Just now, lee59 said:

Ok, so here is one reason why we are now into the Greek alphabet with tropical systems. Sub tropical storm Alpha is going into Portugal.

we're going to have Gamma before the night is over. a record double digit number of storms in September, headed to at least 30 this season.

 

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6 hours ago, bluewave said:

NYC could pull off an early 48°-49° with the favorable northerly flow.

 

326AFFF6-3DAE-4C0E-BD19-BB364EA9B117.thumb.gif.b9a471f6e3ffea000e4977f39bf0dc39.gif

 

First time since the 90s?  I remember you posted earlier that the previous 40s in Sept was back in 1997?  Does that include JFK?

 

 

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1 minute ago, lee59 said:

It has been active, no doubt but I bet decent amount of these storms never would have been named in the past, especially Alpha.

most landfalls that we've ever had too.  It wont equal 1933 or 2005 in terms of hurricanes or majors or ACE, but the TS number is at a historic pace even if you exclude a few of them.

 

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8 minutes ago, lee59 said:

Considering how liberal we have become in naming storms, I think this will be happening far more in the future. It is fine that we name more storms but it makes for bad comparisons when looking back.

ACE is probably  a better metric for comparing activity between seasons but other factors (like how many storms make landfall, the amount of rainfall they deliver, how many are intensifying at landfall, etc., are all factors that should be considered.)

 

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2010's was the warmest decade...the 1950's was the driest...

September decade averages...

Decade...ave temp...rainfall...ave max...ave min...

1870's......65.3......3.41"............................

1880's......66.2......4.18"......86.5......46.1

1890's......67.7......3.38"......89.6......47.0

1900's......68.1......3.84"......86.8......48.4

1910's......66.8......3.09"......89.5......45.6

1920's......67.8......3.54"......91.1......47.2

1930's......68.7......5.15"......90.0......47.9

1940's......68.8......3.70"......91.2......45.5

1950's......68.3......2.36"......89.9......45.6

1960's......67.7......3.85"......90.2......47.2

1970's......68.3......4.73"......90.1......47.1

1980's......68.6......3.58"......90.3......47.5

1990's......68.0......4.18"......88.7......47.6

2000's......68.6......4.91"......86.5......49.7

2010's......70.5......3.67"......92.2......52.7

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The coming weekend will be unseasonably chilly. Even Central Park could see the temperature drop below 50° this weekend for the first time in September since September 24, 2013 when the temperature fell to 47°.

Tomorrow morning's low temperatures will likely be near the following values:

Albany: 36°
Allentown: 41°
Boston: 48°
Bridgeport: 49°
Harrisburg: 47°
Hartford: 42°
Islip: 48°
New York City: 50°
Newark: 49°
Philadelphia: 50°
Poughkeepsie: 40°
Providence: 46°
White Plains: 44°

Generally below normal readings could persist until near the middle of next week. Afterward, temperatures will moderate. There is an increasing possibility that September could wind up on the cool side of normal, which would be an uncommon event in recent cases preceding La Niña winters. Such an outcome is not assured.

The highest rainfall from Hurricane Sally was 29.99" at Orange Beach, AL.

The ENSO Region 1+2 anomaly was -1.0°C and the Region 3.4 anomaly was -1.0°C for the week centered around September 9. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -1.08°C and the ENSO Region 3.4 anomaly has averaged -0.75°C. La Niña conditions have developed and will likely prevail through the remainder of autumn.

The SOI was +17.89.

Today, the preliminary Arctic Oscillation (AO) figure was +0.407.

On September 17, the MJO was in Phase 4 at an amplitude of 1.592 (RMM). The September 16-adjusted amplitude was 1.624.

Since 1990, there have been 11 La Niña events, 6 of which followed an El Niño winter. 10/11 (91%) case saw warmer than normal September. All 6 following an El Niño winter were warmer than normal. September mean temperatures for New York City for those cases were: 11 cases: 69.9°; Subset of 6 cases: 70.8°; Entire 1990-2019 period: 69.0°. The September mean temperature for all La Niña and neutral-cool cases following an El Niño winter (1950-2019: n=13) was 69.9°.

Since 1950, there have been five cases where a La Niña developed during June-July-August or afterward following an El Niño winter. 4/5 (80%) of those cases saw a predominant EPO+/AO+ winter pattern. The most recent such case was 2016-17. 9/10 (90%) of the La Niña winters that followed an El Niño winter featured a predominantly positive EPO.   

Based on sensitivity analysis applied to the latest guidance, there is an implied 49% probability that New York City will have a warmer than normal September. September will likely finish with a mean temperature near 68.1°.

Finally, on September 17, Arctic sea ice extent (JAXA) was 3.735 million square kilometers. It is likely that the summer minimum figure has been reached. That figure was 3.555 million square kilometers (JAXA), which was the second lowest minimum extent on record. 2020 is the second consecutive year with a minimum extent figure below 4.000 million square kilometers and the third such year on record.

 

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8 minutes ago, donsutherland1 said:

The coming weekend will be unseasonably chilly. Even Central Park could see the temperature drop below 50° this weekend for the first time in September since September 24, 2013 when the temperature fell to 47°.

Tomorrow morning's low temperatures will likely be near the following values:

Albany: 36°
Allentown: 41°
Boston: 48°
Bridgeport: 49°
Harrisburg: 47°
Hartford: 42°
Islip: 48°
New York City: 50°
Newark: 49°
Philadelphia: 50°
Poughkeepsie: 40°
Providence: 46°
White Plains: 44°

Generally below normal readings could persist until near the middle of next week. Afterward, temperatures will moderate. There is an increasing possibility that September could wind up on the cool side of normal, which would be an uncommon event in recent cases preceding La Niña winters. Such an outcome is not assured.

The highest rainfall from Hurricane Sally was 29.99" at Orange Beach, AL.

The ENSO Region 1+2 anomaly was -1.0°C and the Region 3.4 anomaly was -1.0°C for the week centered around September 9. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -1.08°C and the ENSO Region 3.4 anomaly has averaged -0.75°C. La Niña conditions have developed and will likely prevail through the remainder of autumn.

The SOI was +17.89.

Today, the preliminary Arctic Oscillation (AO) figure was +0.407.

On September 17, the MJO was in Phase 4 at an amplitude of 1.592 (RMM). The September 16-adjusted amplitude was 1.624.

Since 1990, there have been 11 La Niña events, 6 of which followed an El Niño winter. 10/11 (91%) case saw warmer than normal September. All 6 following an El Niño winter were warmer than normal. September mean temperatures for New York City for those cases were: 11 cases: 69.9°; Subset of 6 cases: 70.8°; Entire 1990-2019 period: 69.0°. The September mean temperature for all La Niña and neutral-cool cases following an El Niño winter (1950-2019: n=13) was 69.9°.

Since 1950, there have been five cases where a La Niña developed during June-July-August or afterward following an El Niño winter. 4/5 (80%) of those cases saw a predominant EPO+/AO+ winter pattern. The most recent such case was 2016-17. 9/10 (90%) of the La Niña winters that followed an El Niño winter featured a predominantly positive EPO.   

Based on sensitivity analysis applied to the latest guidance, there is an implied 49% probability that New York City will have a warmer than normal September. September will likely finish with a mean temperature near 68.1°.

Finally, on September 17, Arctic sea ice extent (JAXA) was 3.735 million square kilometers. It is likely that the summer minimum figure has been reached. That figure was 3.555 million square kilometers (JAXA), which was the second lowest minimum extent on record. 2020 is the second consecutive year with a minimum extent figure below 4.000 million square kilometers and the third such year on record.

 

Has there ever been a La Nina winter where the month of September winds up being below normal? If so, what was that winter like?

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The next 8 days are averaging 67degs.      Make it 62degs., or -5.0.

52*!(44%RH) here at 6:00am, m. clear.   51* at 6:30am        56* by 11am.        60* by 2pm.      63* by 3pm.     64*(30%RH) by 3:30pm.

No precipitation till the 29th +/- a day, or any model.      EURO now ups the T's for the next 10 days, while the GFS backs them down.

Tropics quieting down:    26N 93W,  25N 59W-still getting stronger, but I am just a strawman, 13N 37W-going nowhere?

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The low of 50° in NYC was the coldest September temperature since 2013. Early Sunday could be a degree or two cooler. 
 

Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Sep
Click column heading to sort ascending, click again to sort descending.
Year
Lowest Min Temperature 
Missing Count
2020 50 11
2019 52 0
2018 54 0
2017 54 0
2016 54 0
2015 56 0
2014 52 0
2013 47 0
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Morning thoughts...

The coldest air so far this season now covers the region. Today will be partly sunny and very cool for the season. The temperature will likely struggle toward the middle 60s across the region. Likely high temperatures around the region include:

New York City (Central Park): 64°
Newark: 65°
Philadelphia: 65°

A warmup will likely commence toward the middle of next week.

In terms of verification, here's how last evening's estimates worked out:

Albany: 36°; Actual: 33°  
Allentown: 41°; Actual: 39°
Boston: 48°; Actual: 46°
Bridgeport: 49°; Actual: 47°
Harrisburg: 47°; Actual: 43°
Hartford: 42°; Actual: 37°
Islip: 48°; Actual: 49°
New York City: 50°; Actual: 50°
Newark: 49°; Actual: 48°
Philadelphia: 50°; Actual: 48°
Poughkeepsie: 40°; Actual: 36°
Providence: 46°; Actual: 45°
White Plains: 44°; Actual: 42°

Average Error: 2.2°

 

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