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September 2020 wx discussion


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21 minutes ago, SACRUS said:

Coldest should be Sun night - Monday.  850s forecast at <0C.  Temps rebound by 9/23 - 9/25 before next cool down 9/26-9/27.  Back and forth with chance for cutoff ULL towards next month into the MW.  

Doesn't look like a cooldown on the 26th-27th to me. Models are showing maybe a very brief minor cooldown on friday the 25th after the warmth of the 23rd-24th, and then actually warming back up the weekend of the 26th-27th. Could be looking at 80 degrees sunday the 27th.

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8 minutes ago, winterwx21 said:

Doesn't look like a cooldown on the 26th-27th to me. Models are showing maybe a very brief minor cooldown on friday the 25th after the warmth of the 23rd-24th, and then actually warming back up the weekend of the 26th-27th. Could be looking at 80 degrees sunday the 27th.

It's complicated and Teddy's evolution will play a role in the future pattern.

Looks like it'll cause the NAO to go negative.

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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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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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