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September 2019 General Discussions & Observations Thread


Rtd208
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Ahead of a cold front, much of the region saw temperatures in the lower to middle 80s. Today was Washington, DC's 60th 90° or warmer day this year, which is the 3rd most such days during a year. Only 1980 and 2010, both with 67 such days, had more.

A generally warmer than normal pattern will likely prevail into the start of October with some fluctuations. There is potential for much above normal warmth to start October.

The PNA is forecast to plunge in coming days. Typically, a strongly negative PNA (-1.50 or below) during the October 1-3 period has translated into readings averaging 2°-4° above normal in the Middle Atlantic and southern New England regions. The warmth has been even more pronounced when the strongly negative PNA has coincided with a negative SOI.

A period of cooler than normal readings will likely move into the region during the latter part of the first week of October. Nevertheless, a warmer than normal October appears likely. Events during September, including the SOI's falling to -35.30 on September 19 and the ongoing evolution toward a generally positive AO regime, favor a warmer than normal October based on past outcomes.

Courtesy of low sea ice, abnormal warmth continued to prevail in northern Alaska. There is a near 100% implied probability that Utqiagvik (formerly Barrow) will record its warmest September on record. It is likely that Utqiagvik will register its first 40.0° mean temperature for September. A 40.0° mean temperature would rank 30th out of 99 years for the warmest August on record. The existing monthly record of 37.7° has stood since 1998.

Earlier today, Reykjavik tied its September record high temperature of 64°.

The ENSO Region 1+2 anomaly was -1.3°C and the Region 3.4 anomaly was -0.2°C for the week centered around September 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.77°C and the ENSO Region 3.4 anomaly has averaged -0.16°C. The recent strong cooling in Region 1+2 indicates that the prospects for a neutral-cool ENSO during the winter have continued to increase. Such a scenario is now more likely than not.

Since 1991 when weekly ENSO region data was available, five years have seen September record 2 or more weeks with -1.0°C or cooler weekly anomalies in Region 1+2: 1996, 1999, 2007, 2010, and 2017. 4/5 (80%) of those cases went on to feature warm December-February temperature anomalies in the Middle Atlantic and southern New England regions. Those cases include La Niña winters. However, the larger pool of neutral-cool ENSO winters, many of which predate the weekly ENSO regional data, have often featured frequent Atlantic blocking. For now, there is a mixed winter signal.

The SOI was +2.38 today.

Today, the preliminary Arctic Oscillation (AO) figure was +1.007.

Since 1950, there have been five prior cases when the AO averaged -0.500 or below in both July and August: 1950, 1958, 1960, 1968, and 2015. The average temperature for September was 69.1° (69.8° after adjusting for ongoing warming) and 58.9° (59.6° adjusted) for September through November in New York City. The 1981-2010 baseline normal figures are 68.0° and 57.5° respectively. The majority of cases saw a warmer than normal September and all cases featured a warmer than normal fall.

A warmer than normal September is now extremely likely. A warmer than normal fall remains likely. The potential for autumn 2019 to rank among the 30 warmest cases on record has increased in recent weeks. For New York City, that would translate into a September-November mean temperature of at least 58.8°.

On September 25, the MJO was in Phase 1 at an amplitude of 2.717 (RMM). The September 24-adjusted amplitude was 2.540.

Based on sensitivity analysis applied to the latest guidance, the implied probability of New York City having a warmer than normal September is approximately >99% and the probability of a monthly mean temperature of 70.0° or above is 57%. Should September 2019 have a mean temperature of 70.0° or above, 2019 would be the 5th consecutive year with such September warmth. Prior to the current stretch, the record was 2 consecutive years (1930 and 1931; 1970 and 1971; 1979 and 1980; and, 2010 and 2011).

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The last 4 days of September are averaging 69degs. or about 6degs. AN.

Month to date is  +1.8[70.5].       September should end near   +2.3[70.3].

63.1* here at 6am.    66.5* by 10am.   68.0* by Noon.    Still 68.0* at 1pm-not a late beach day here despite sun.      70.0* at 2pm.   70.7* at 3pm.

Any 90* reading here at the opening of Oct., appears to have faded.      EURO with a lone 91* on the 2nd, surrounded by upper 70's.   GFS never really showed 90's, even with its bias---now is 89*, 88*, for the 2nd, 3rd.

At any rate, the GFS is BN starting the 4th., with 850mb T's appropriate for the start of Nov., it would appear.

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0.09 rain yesterday.  Another week of of warmth and temps should over perform (1 or r 90s)  but again brunt and core of the late season heat a bit to our west and south. 

Oct 5 - 7 look to feature a sharp contrast to the prior weeks warmth especially in New England, then followed by more of a back and forth progression to some warm days and steady stream of cold front.s 

 

 

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7 hours ago, SACRUS said:

0.09 rain yesterday.  Another week of of warmth and temps should over perform (1 or r 90s)  but again brunt and core of the late season heat a bit to our west and south. 

Oct 5 - 7 look to feature a sharp contrast to the prior weeks warmth especially in New England, then followed by more of a back and forth progression to some warm days and steady stream of cold front.s 

 

 

Euro's much more reluctant to cool us down vs Gfs though it's inevitable with the high pressing south.

More of a pattern shift than a change right now. Nothing to suggest BN temps or stormy weather.

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Islip still in 1st place for driest September with just 3 days to go.

Time Series Summary for ISLIP-LI MACARTHUR AP, NY - Month of Sep
Click column heading to sort ascending, click again to sort descending.
Rank
Year
Total Precipitation 
Missing Count
1 2019 0.61 3
2 1985 0.81 0
3 1986 0.82 0
4 1965 1.01 0
5 1982 1.12 0
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The last 3 days of September are averaging 70degs., or 7degs. AN.

Month to date is  +1.8[70.4].        September should end  near  +2.4[70.4].

The first 3 days of Oct:

GFS.        80  90  83.

EURO.     78  92  82.

Their ensembles are both much lower.

65.5* here at 6am.   69.0* by 10am.

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