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Sunday, September 21, 2025

September 21, 2025

BLUE HILL METEOROLOGICAL OBSERVATORY MILTON, MASSACHUSETTS ELEVATION 635 FEET, 10 MILES SSW OF BOSTON, MA SUNDAY, SEPTEMBER 21, 2025 ALL TIMES ARE…

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BLUE HILL METEOROLOGICAL OBSERVATORY
MILTON, MASSACHUSETTS
ELEVATION 635 FEET, 10 MILES SSW OF BOSTON, MA

SUNDAY, SEPTEMBER 21, 2025
ALL TIMES ARE IN EASTERN STANDARD TIME (EST)
SUNRISE: 0531E
SUNSET:  1743E

CONTINUED COOLER TEMPERATURES TODAY WITH INCREASING
AFTERNOON CLOUDS….

Today started off with bright sunshine and crisp, blue skies
with thinly scattered cirrus clouds. As the morning continued,
cumulus and cirrus clouds increased in the area, giving us
a partly to mostly cloudy afternoon. With light winds from
the east, and dry air overhead, today has felt like another
beautiful autumn day. As tomorrow is the first day of the
autumnal equinox, it is rather fitting.

Temperatures dipped around 52F during the early morning hours
here, and quickly warmed to the upper 60’s by 7am. Since then,
we have only increased a few degrees above that, thanks to the
dry air mass over the region, and a light, but noticeable sea
breeze. Dew points started in the upper 40’s this morning and
got to the mid 50’s by afternoon.

There were periods of calm wind conditions during the overnight
hours, and since then, winds have remained light and mostly out
of the east. The average speed for the day is only around 4mph.
The peak gust for the day is 16mph, which occurred just after
11:00am this morning.

Visibility has varied between 50-60 miles for most of the day
today.

The maximum temperature so far today is 67F degrees, which is
4 degrees below the normal high of 71F. The minimum temperature
since midnight is 52F degrees, which is 2 degrees below the
normal low of 54F.

————————————————————–

Today’s Observations:

7 A.M.
Weather: Thinly scattered cirrus, few cumulus distant NNE-ENE
Temperature: 59F; Dew Point: 43F; Relative Humidity: 56%
Wind: Calm
Sea-level pressure: 1029.6 mb; 30.40 in. Hg: rising, then more
slowly
Visibility: 50 miles
6-hr Max temp: 59F
6-hr Min temp: 52F
24-hr Precip: 0.00 inches
BHO SA 1155 250 -SCT 50 296/59/43/0000/040/ FEW CU DSNT NNE-ENE
WND CALM/ 8/201 51011 10059 20052

10 A.M.
Weather: Scattered cumulus, broken cirrus
Temperature: 63F; Dew Point: 50F; Relative Humidity: 63%
Wind: ESE @ 6 kts, wind light
Sea-level pressure: 1029.4 mb; 30.40 in. Hg: rising, then
falling
Visibility: 60 miles
3-hr Precip: 0.00 inches
BHO SA 1455 45 SCT E250 BKN 60 294/63/50/1106/040/ WND LGT/
8/201 58002

1 P.M.
Weather: Scattered cumulus, broken cirrus
Temperature: 67F Dew Point: 54F; Relative Humidity: 62%
Wind: E @ 4 kts, wind light
Sea-level pressure: 1028.2 mb; 30.36 in. Hg: falling, then
more rapidly
Visibility: 60 miles
6-hr Max temp: 67F
6-hr Min temp: 59F
6-hr Precip: 0.00 inches
BHO SA 1755 30 SCT E250 BKN 60 282/67/54/1004/036/ WND LGT/
8/201 58012 10067 20059

————————————————————–

SUMMARY FOR SATURDAY, SEPTEMBER 20, 2025

TEMPERATURE (DEGREES F)
MAX…….67   NORMAL…..71
MIN…….51   NORMAL…..54
MEAN……59   NORMAL…..63

DEPARTURE FROM 30-YEAR (1991-2020) NORMAL…………….-4
TOTAL DEPARTURE FOR THE MONTH………………………-15 [-1.0 DEGREES/DAY]

HEATING DEGREE DAYS (SEASON: JUL 2025 THRU JUN 2026)
TOTAL HEATING UNITS FOR YESTERDAY……………..6  DEPARTURE……..+2
TOTAL HEATING UNITS FOR THE MONTH…………….32  DEPARTURE…….-11
TOTAL HEATING UNITS FOR THE SEASON……………52  DEPARTURE……..-9
TOTAL HEATING UNITS LAST SEASON TO DATE……….25  DEPARTURE…….+27

COOLING DEGREE DAYS (SEASON JAN 2025 THRU DEC 2025)
TOTAL COOLING UNITS FOR YESTERDAY……………..0  DEPARTURE……..-2
TOTAL COOLING UNITS FOR THE MONTH…………….38  DEPARTURE…….-25
TOTAL COOLING UNITS FOR THE SEASON…………..710  DEPARTURE…….+51
TOTAL COOLING UNITS LAST SEASON TO DATE………753  DEPARTURE…….-43

PEAK WIND GUST (MPH):
Note: Instruments designated #1 = Main Tower, #2 = South Tower,
F420C, Contacting, Merlin, and Richards are all on Main Tower.
E=Estimated

F420C (Official)………..20 SE   @   07:52 P.M.
VECTOR #1 (1-Sec)……….19 SE   @   07:52 P.M.
VECTOR #2 (1-Sec)……….18 NNE  @   01:48 A.M.
DAVIS #1……………….16 NNE  @   12:17 A.M.
DAVIS #2 ………………18 SE   @   07:52 P.M.
RMY #1 (Instantaneous)…..18 NNE  @   01:50 P.M.
RMY #2 (Instantaneous)…..19 SE   @   08:02 P.M.
MERLIN…………………16 SSE
RICHARDS (C5C) (Inst)……17 SE   @   08:00 P.M.

FASTEST MILE:
CONTACTING ANEMOMETER/OFFICIAL………………13 SE   @   07:55 P.M.
MAXIMUM 2-MINUTE VECTOR #1 AVERAGE…………..14 SE   @   07:19 P.M.
MAXIMUM 2-MINUTE VECTOR #2 AVERAGE…………..14 SE   @   08:00 P.M.
MAXIMUM 2-MINUTE DAVIS #1 AVERAGE……………13 SE   @   07:19 P.M.
MAXIMUM 2-MINUTE DAVIS #2 AVERAGE……………14 SE   @   07:58 P.M.
MAXIMUM 2-MINUTE RMY #1 AVERAGE……………..13 SE   @   07:55 P.M.
MAXIMUM 2-MINUTE RMY #2 AVERAGE……………..14 SE   @   08:00 P.M.
MAXIMUM 2-MINUTE RICHARDS (C5C) AVERAGE………14 SE   @   08:00 P.M.

AVERAGE WIND SPEED AND DIRECTION:
CONTACTING/OFFICIAL………7.6 SE [183 total miles] VECTOR #1……………….8.0
VECTOR #2……………….8.6
DAVIS #1………………..8.1 E
DAVIS #2………………..8.3 E
RMY #1………………….7.8 E
RMY #2………………….8.5 ENE
RICHARDS (C5C)…………..8.4

PRECIPITATION (INCHES) THROUGH THIS MORNING (EST):
TOTAL PRECIPITATION 24 HRS ENDING 7 A.M……..0.00 DEPARTURE…..-0.15
TOTAL PRECIPITATION FOR THE MONTH…………..2.58 DEPARTURE…..+0.02
TOTAL PRECIPITATION FOR THE YEAR (2025)…….33.91 DEPARTURE…..-3.26

————————————————————–

PRELIMINARY CLIMATE SUMMARY FOR SEPTEMBER CALENDAR DAY DATA
DATE: MAX/MIN/MEAN/DEP/PRECIP/SUN(MIN)/SUN(%)/PEAK GUST/VEC1/RMY GUST
PEAK GUST: F420C (Official)
VEC1: Vector #1 1-second gust
RMY:  R.M. Young #1 wind gust recording system (Instantaneous)
TSTM: Thunderstorm day (thunder heard some time during day)
….: Data not yet available, records not finalized
M:    Missing data

9/1   73/55/64/-5/0.00/221/28            23 NE  VEC1 23 ENE RMY 23
9/2   77/58/68/-1/0.00/714/91            18 ESE VEC1 19 ESE RMY 18
9/3   78/57/68/0/0.00/719/92             21 SSW VEC1 21 SSW RMY 21
9/4   81/56/69/+1/0.00/694/89            26 SSW VEC1 27 SSW RMY 28
9/5   82/63/73/+5/0.12/404/52            30 SSW VEC1 31 SSW RMY 33
9/6   84/64/74/+6/1.05/457/59            55 W   VEC1 55 W   RMY 57 TSTM
9/7   64/56/60/-7/0.97/000/00            16 WNW VEC1 16 NNE RMY 15
9/8   68/49/59/-8/0.00/508/66            21 NW  VEC1 21 NW  RMY 24
9/9   70/53/62/-5/0.00/697/91            22 ENE VEC1 23 E   RMY 23
9/10  65/54/60/-6/0.00/183/24            24 NE  VEC1 25 NE  RMY 25
9/11  77/51/64/-2/0.00/714/94            21 N   VEC1 17 N   RMY 18
9/12  71/56/64/-2/0.00/735/97            24 ENE VEC1 24 NNE RMY 23
9/13  76/55/66/+1/T/634/84               26 S   VEC1 26 S   RMY 25
9/14  79/57/68/+3/0.00/572/76            15 NE  VEC1 15 SW  RMY 15
9/15  72/57/65/0/0.00/689/92             20 N   VEC1 19 N   RMY 18
9/16  71/55/63/-1/0.00/403/54            20 E   VEC1 19 ESE RMY 19
9/17  71/55/63/-1/T/424/57               22 E   VEC1 22 E   RMY 21
9/18  75/61/68/+5/0.44/252/34            20 S   VEC1 20 S   RMY 20 TSTM
9/19  80/57/69/+6/0.00/715/97            24 N   VEC1 24 N   RMY 23
9/20  67/51/59/-4/0.00/…/..            20 SE  VEC1 19 SE  RMY 18

9/21 The low since midnight is 52F, the daily normal low is 54F.

————————————————————–

SEPTEMBER DAILY RECORDS TO DATE

NONE.

————————————————————–

DAILY EXTREMES
Temperature and precipitation records back to 1885, and
wind records back to 1940 (e = estimated)

RECORDS FOR SEPTEMBER 21
HIGH 91 IN 1895
LOW 35 IN 1929, 1956, 1962
PRECIP 5.58 INS IN 1961 (HURRICANE ESTHER; RETURNED AS TS SEPT 25-26TH)
PEAK GUST 186 MPH S IN 1938 (GREAT NEW ENGLAND HURRICANE; CALCULATED GUST, STATION RECORD)

RECORDS FOR SEPTEMBER 22
HIGH 90F IN 1895, 1914
LOW 30F IN 1904 (Earliest freeze)
PRECIP 1.16 INCHES IN 2001
PEAK GUST 60 MPH SSW IN 1989

TODAY’S REPORT PREPARED BY: Amanda Joly

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Blue Hill Observatory & Science Center · Legal

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Please read the full Policy before accessing Observatory data · Effective January 1, 2025

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Effective January 1, 2025 · Milton, Massachusetts · bluehill.org
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