During my time taking classes as part of Penn State University’s Undergraduate Certificate in Weather Forecasting, we were taught that understanding the climatology of the location you are interested in is an important prerequisite for making accurate forecasts. This post continues on this theme, adding a climatology for September.

Other Month’s Climatologies

January
February
March
April
May
June
July
August
October
November
December

Station Basic Information

City Name / Station ID: New York, NY (LaGuardia Airport – KLGA)

Local Geography and Topography

Station Elevation: 10 feet above sea level.

Station Location: LaGuardia Airport (KLGA) is situated on the north shore of Queens along the East River, approximately 6 miles east-northeast of Midtown Manhattan.

Important Topographical Features: New York City is located in the extreme southeastern corner of New York State, bordering suburban New Jersey and Connecticut. These suburban regions combined with those in Long Island comprise the Greater New York City Metropolitan Area, which is the most populous urban agglomeration in the United States and one of the populous urbanized areas in the world with an estimated population of 18 million. New York City itself sprawls across the coastal plain around the Hudson River estuary. The terminal moraine formed by glaciers of the last Ice Age result in a ridge of higher terrain that cuts a swath from southwest to northeast across the boroughs from northern Staten Island, northern Brooklyn, southwestern through central and northeastern Queens. Otherwise, the city itself is low lying. This ridge varies in height between 200-400 feet, rising sharply from south to north, but tapering more gently north. North and west of the city (about 30-50 miles away), lie significant elevations of the Catskills (north), Poconos (west), Taconics that are part of the broader Appalachian Mountain Range. The elevations of the lower foothills can range from 1000-1500 feet. Some of the elevations in the Poconos and Catskills, west and north of KLGA respectively, peak between 2000-3000 feet. The open expanse of the Atlantic Ocean lies south of KLGA and New York City. Long Island Sound also lies east-northeast. The vast urbanized area of the NYC metropolitan region has significant effects on local microclimates via differential heating (urban heat island effect). KLGA is in a low-lying area sensitive to UHI effects and marine influences.

Per the Local Climatological Data report from the National Weather Service:

On winter mornings, ocean temperatures which are warm relative to the land reinforce the effect of the city heat island and low temperatures are often 10-20 degrees lower in the inland suburbs than in the central city. The relatively warm water temperatures also delay the advent of winter snows. Conversely, the lag in warming of water temperatures keeps spring temperatures relatively cool. One year-round measure of the ocean influence is the small average daily variation in temperature.

National Weather Service – NYC Office

Wind Patterns

Below is a wind rose – you can read more about how to interpret this chart here.

Frequency (percentage) of the single most common wind direction: Due northeast (9.5%).

Directions that are most and least common: Most common wind directions include due south (9%), due southwest (8.5%), and northwest (8%). Least common wind directions are east-southeast (1.5%), due southeast (2.5%), and due east (3.5%).

Direction(s) most likely to produce the fastest winds: Winds of 16.5-21.4 knots are most frequently found coming from due northeast, and due northeast. North-northwest, east-northeast, and due south directions can also see less frequent winds over 21.4 knots.

Direction(s) least likely to produce the fastest winds: As is the case with several other months, the least common wind directions of due east, east-southeast, and due southeast also rarely seen winds in excess of 16.4 knots.

Impacts of wind direction on local weather: September’s wind profile sees a shift away from the general pattern of the summer months preceding it (June, July, August) during which southerly winds are predominant, and during which due south is the single most common wind direction. April is the last calendar month when due south isn’t the single most common wind direction, so it takes quite a bit of time in order for winds to shift off this summer pattern.

The most common wind directions in September are almost evenly split between northeasterly and northwesterly and southerly and southwesterly winds in percentage terms of frequency. Northwesterly winds are notably more frequent, and faster northeasterly and northwesterly winds start to appear in September as opposed to the summer months. Northwesterly winds in general will bring cooler, drier Canadian air into the region following cold fronts. Northeasterly winds, on the other hand, are related to backdoor cold fronts sweeping from the Canadian Maritimes, the onshore flow ahead of an advancing warm front, or a passing coastal storm.

The continued downward trend in southerly winds is likely a reflection of the diminishing influence of sea breezes as average land temperatures cool while average sea surface temperatures are still close to their peak (though also cooling). The narrowing gap between these two will tend to reduce the potential for sea breeze circulations to set up. However, these sea breezes can still exert an influence on local temperature and can still provide boundaries for convection. Southwesterly winds are also similarly capable of bringing in oppressive heat, as seen in the temperature section below.

Maximum observed two-minute wind speed for the month: 44 knots (51 mph)

Temperature and Precipitation Averages/Records

Temperature units are in Fahrenheit and precipitation is in inches.

Worth noting: September can still offer up oppressive heat, especially in the first half of the month. The monthly all-time record high of 102°F is also the second highest record temperature recorded for the year at KLGA (August has the hottest record high: 104°F). September’s monthly precipitation record of 4.63″ in one day is also has the 3rd highest single-day precipitation record after April and August. While it can get quite hot in September, it’s also possible for temperatures to get cold too, with the record low for the month in the low-40s! Average high temperatures dip back below 80°F and average lows drop below 60°F again in September after the summer months, marking a definite fall feel.

‘Date	Normal High	Normal Low	Record High	Record Low	Record Lowest Max	Record Highest Min	Normal Precip	Record Precip
1	81	67	96	55	67	78	0.11	1.20
2	81	66	102	56	65	81	0.12	2.88
3	80	66	95	54	68	77	0.12	2.33
4	80	66	93	54	66	80	0.12	3.12
5	80	66	93	54	67	79	0.12	1.00
6	80	65	96	53	62	79	0.12	3.21
7	79	65	90	53	66	74	0.12	2.37
8	79	65	95	54	65	76	0.12	3.85
9	79	64	93	53	65	77	0.11	0.56
10	78	64	95	50	67	76	0.12	1.47
11	78	64	96	51	64	78	0.12	2.93
12	78	63	94	52	68	75	0.12	3.63
13	77	63	93	50	61	75	0.13	2.93
14	77	63	92	48	63	74	0.13	2.93
15	77	62	91	49	59	76	0.13	0.82
16	76	62	95	48	62	73	0.12	4.63
17	76	62	95	48	61	79	0.12	1.65
18	76	61	89	48	64	72	0.13	1.99
19	75	61	92	49	61	72	0.13	1.62
20	75	60	90	46	61	74	0.13	1.72
21	75	60	89	43	59	73	0.13	3.02
22	74	60	93	47	56	73	0.12	1.00
23	74	59	93	42	57	77	0.12	2.14
24	73	59	91	44	52	73	0.12	1.34
25	73	59	90	42	57	72	0.13	2.84
26	73	58	90	44	57	72	0.12	3.19
27	72	58	90	43	56	73	0.13	2.72
28	72	57	84	42	56	72	0.14	3.27
29	71	57	86	43	58	72	0.14	1.85
30	71	57	88	43	56	71	0.14	1.80
Range	71-81	57-67	84-102	42-56	52-68	71-81	0.11-0.14	0.56-4.63