WEATHER FOR BUSINESS

We supply weather data to businesses

Free Weather Plugin

Add this forecast to your website



Local Weather

Basseterre 14 Day Long Range Forecast

14 Day weather providing an extended long range forecast outlook for Basseterre

St. Kitts And Nevis

Long range weather outlook for Basseterre includes 14 day forecast summary:

The forecast for Basseterre in the coming two weeks is predicting the average daytime maximum temperature will be around 32°C, with a high for the two weeks of 34°C expected on the afternoon of Friday 19th. The mean minimum temperature will be 28°C, dipping to its lowest on the morning of Sunday 28th at 27°C. The fortnight ahead will have some days seeing a little precipitation and some days with rain. The current forecast indicates Saturday 27th will have the most precipitation with an accumulation of around 7.0mm. On the whole winds are likely to be moderate.

DayLocal TimeDirSpeed/
Gust
Temp/
Feels Like
HumidityPressureCloud AmountPrecip AmountWeather
Thu 18
Sep
02:00

ESE
ESE

16 / 22 mph 83 / 90°F 74% 1011 mb
Low level cloud: 11%
Mid level cloud: 24%
High level cloud: 26%
Most Significant Cloud Type: low
22%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
05:00

ESE
ESE

16 / 25 mph 81 / 87°F 76% 1011 mb
Low level cloud: 17%
Mid level cloud: 22%
High level cloud: 15%
Most Significant Cloud Type: low
26%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
08:00

ESE
ESE

13 / 19 mph 84 / 89°F 75% 1013 mb
Low level cloud: 30%
Mid level cloud: 20%
High level cloud: 5%
Most Significant Cloud Type: low
37%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
11:00

ESE
ESE

11 / 15 mph 89 / 101°F 74% 1013 mb
Low level cloud: 12%
Mid level cloud: 25%
High level cloud: 2%
Most Significant Cloud Type: low
20%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
14:00

SE
SE

9 / 11 mph 93 / 110°F 74% 1012 mb
Low level cloud: 7%
Mid level cloud: 16%
High level cloud: 10%
Most Significant Cloud Type: low
13%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
17:00

N
N

3 / 6 mph 89 / 94°F 70% 1011 mb
Low level cloud: 9%
Mid level cloud: 26%
High level cloud: 62%
Most Significant Cloud Type: low
26%
Expect 0.2 In of precipitation over the past 3 hours.
0.2 In
20:00

NE
NE

9 / 12 mph 84 / 90°F 67% 1013 mb
Low level cloud: 0%
Mid level cloud: 15%
High level cloud: 7%
Most Significant Cloud Type: medium
15%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
23:00

E
E

11 / 17 mph 83 / 89°F 69% 1013 mb
Low level cloud: 22%
Mid level cloud: 16%
High level cloud: 0%
Most Significant Cloud Type: low
27%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Fri 19
Sep
20:00

ESE
ESE

6 / 7 mph 87 / 98°F 68% 1014 mb
Low level cloud: 2%
Mid level cloud: 10%
High level cloud: 11%
Most Significant Cloud Type: medium
15%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
23:00

ESE
ESE

9 / 10 mph 86 / 95°F 73% 1014 mb
Low level cloud: 20%
Mid level cloud: 9%
High level cloud: 21%
Most Significant Cloud Type: low
25%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Sat 20
Sep
02:00

ESE
ESE

9 / 11 mph 83 / 90°F 75% 1013 mb
Low level cloud: 61%
Mid level cloud: 8%
High level cloud: 75%
Most Significant Cloud Type: low
72%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
05:00

ESE
ESE

8 / 12 mph 82 / 88°F 74% 1013 mb
Low level cloud: 34%
Mid level cloud: 8%
High level cloud: 19%
Most Significant Cloud Type: low
38%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
08:00

ESE
ESE

9 / 12 mph 86 / 91°F 75% 1015 mb
Low level cloud: 41%
Mid level cloud: 6%
High level cloud: 3%
Most Significant Cloud Type: low
43%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
11:00

SE
SE

12 / 13 mph 87 / 97°F 75% 1015 mb
Low level cloud: 61%
Mid level cloud: 6%
High level cloud: 5%
Most Significant Cloud Type: low
63%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
14:00

SE
SE

9 / 10 mph 90 / 100°F 74% 1014 mb
Low level cloud: 55%
Mid level cloud: 6%
High level cloud: 6%
Most Significant Cloud Type: low
57%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
17:00

ESE
ESE

6 / 6 mph 89 / 98°F 70% 1013 mb
Low level cloud: 36%
Mid level cloud: 6%
High level cloud: 4%
Most Significant Cloud Type: low
38%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
20:00

E
E

9 / 10 mph 85 / 94°F 71% 1015 mb
Low level cloud: 52%
Mid level cloud: 6%
High level cloud: 17%
Most Significant Cloud Type: low
56%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
23:00

ESE
ESE

13 / 17 mph 84 / 92°F 73% 1015 mb
Low level cloud: 47%
Mid level cloud: 6%
High level cloud: 0%
Most Significant Cloud Type: low
48%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Sun 21
Sep
02:00

ESE
ESE

12 / 16 mph 84 / 92°F 76% 1013 mb
Low level cloud: 56%
Mid level cloud: 6%
High level cloud: 0%
Most Significant Cloud Type: low
57%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
05:00

ESE
ESE

12 / 17 mph 82 / 87°F 72% 1014 mb
Low level cloud: 45%
Mid level cloud: 7%
High level cloud: 0%
Most Significant Cloud Type: low
47%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
08:00

E
E

11 / 13 mph 86 / 91°F 74% 1015 mb
Low level cloud: 27%
Mid level cloud: 4%
High level cloud: 0%
Most Significant Cloud Type: low
28%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
11:00

ESE
ESE

12 / 14 mph 89 / 101°F 74% 1015 mb
Low level cloud: 28%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
28%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
14:00

ESE
ESE

11 / 12 mph 92 / 108°F 72% 1014 mb
Low level cloud: 48%
Mid level cloud: 1%
High level cloud: 0%
Most Significant Cloud Type: low
48%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
17:00

ESE
ESE

10 / 11 mph 91 / 104°F 70% 1013 mb
Low level cloud: 3%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
2%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
20:00

E
E

12 / 14 mph 87 / 99°F 73% 1014 mb
Low level cloud: 59%
Mid level cloud: 2%
High level cloud: 0%
Most Significant Cloud Type: low
59%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
23:00

E
E

14 / 16 mph 85 / 95°F 76% 1014 mb
Low level cloud: 49%
Mid level cloud: 6%
High level cloud: 0%
Most Significant Cloud Type: low
51%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Mon 22
Sep
02:00

E
E

16 / 21 mph 83 / 91°F 75% 1013 mb
Low level cloud: 43%
Mid level cloud: 19%
High level cloud: 5%
Most Significant Cloud Type: low
49%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
05:00

E
E

15 / 23 mph 82 / 88°F 75% 1013 mb
Low level cloud: 54%
Mid level cloud: 21%
High level cloud: 31%
Most Significant Cloud Type: low
65%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
08:00

E
E

15 / 20 mph 85 / 90°F 73% 1014 mb
Low level cloud: 41%
Mid level cloud: 29%
High level cloud: 17%
Most Significant Cloud Type: low
53%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
11:00

E
E

18 / 22 mph 87 / 97°F 73% 1015 mb
Low level cloud: 36%
Mid level cloud: 24%
High level cloud: 16%
Most Significant Cloud Type: low
46%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
14:00

E
E

16 / 19 mph 89 / 101°F 73% 1013 mb
Low level cloud: 55%
Mid level cloud: 27%
High level cloud: 8%
Most Significant Cloud Type: low
65%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
17:00

ENE
ENE

16 / 18 mph 89 / 101°F 76% 1012 mb
Low level cloud: 29%
Mid level cloud: 22%
High level cloud: 7%
Most Significant Cloud Type: low
37%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
20:00

ENE
ENE

18 / 24 mph 86 / 97°F 78% 1013 mb
Low level cloud: 70%
Mid level cloud: 12%
High level cloud: 8%
Most Significant Cloud Type: low
75%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
23:00

E
E

18 / 23 mph 84 / 93°F 75% 1014 mb
Low level cloud: 30%
Mid level cloud: 15%
High level cloud: 8%
Most Significant Cloud Type: low
35%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Tue 23
Sep
02:00

E
E

16 / 23 mph 83 / 89°F 73% 1012 mb
Low level cloud: 21%
Mid level cloud: 5%
High level cloud: 2%
Most Significant Cloud Type: low
23%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
05:00

E
E

17 / 27 mph 82 / 89°F 77% 1013 mb
Low level cloud: 64%
Mid level cloud: 14%
High level cloud: 6%
Most Significant Cloud Type: low
69%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
08:00

E
E

17 / 26 mph 84 / 89°F 75% 1014 mb
Low level cloud: 20%
Mid level cloud: 14%
High level cloud: 14%
Most Significant Cloud Type: low
26%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
11:00

ESE
ESE

15 / 21 mph 86 / 92°F 74% 1015 mb
Low level cloud: 63%
Mid level cloud: 10%
High level cloud: 0%
Most Significant Cloud Type: low
66%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
14:00

ESE
ESE

14 / 17 mph 87 / 94°F 73% 1014 mb
Low level cloud: 34%
Mid level cloud: 20%
High level cloud: 0%
Most Significant Cloud Type: low
40%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
17:00

ESE
ESE

15 / 19 mph 86 / 94°F 75% 1013 mb
Low level cloud: 13%
Mid level cloud: 26%
High level cloud: 0%
Most Significant Cloud Type: low
21%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
20:00

E
E

20 / 28 mph 84 / 92°F 76% 1015 mb
Low level cloud: 22%
Mid level cloud: 7%
High level cloud: 1%
Most Significant Cloud Type: low
24%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
23:00

ESE
ESE

21 / 30 mph 83 / 90°F 74% 1015 mb
Low level cloud: 58%
Mid level cloud: 8%
High level cloud: 1%
Most Significant Cloud Type: low
61%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Wed 24
Sep
02:00

ESE
ESE

17 / 25 mph 83 / 89°F 75% 1014 mb
Low level cloud: 36%
Mid level cloud: 15%
High level cloud: 6%
Most Significant Cloud Type: low
42%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
05:00

ESE
ESE

17 / 26 mph 82 / 88°F 74% 1014 mb
Low level cloud: 49%
Mid level cloud: 20%
High level cloud: 33%
Most Significant Cloud Type: low
60%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
08:00

E
E

17 / 24 mph 84 / 89°F 73% 1015 mb
Low level cloud: 12%
Mid level cloud: 35%
High level cloud: 8%
Most Significant Cloud Type: medium
68%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
11:00

ESE
ESE

18 / 23 mph 85 / 94°F 76% 1016 mb
Low level cloud: 60%
Mid level cloud: 46%
High level cloud: 7%
Most Significant Cloud Type: low
77%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
14:00

ESE
ESE

19 / 23 mph 87 / 97°F 76% 1014 mb
Low level cloud: 58%
Mid level cloud: 58%
High level cloud: 13%
Most Significant Cloud Type: low
79%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
17:00

ESE
ESE

20 / 23 mph 87 / 96°F 76% 1014 mb
Low level cloud: 59%
Mid level cloud: 22%
High level cloud: 14%
Most Significant Cloud Type: low
68%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
20:00

ESE
ESE

20 / 26 mph 84 / 94°F 78% 1015 mb
Low level cloud: 68%
Mid level cloud: 14%
High level cloud: 19%
Most Significant Cloud Type: low
74%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
23:00

ESE
ESE

21 / 28 mph 83 / 92°F 78% 1015 mb
Low level cloud: 76%
Mid level cloud: 18%
High level cloud: 22%
Most Significant Cloud Type: low
85%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
DayLocal TimeDirSpeed/
Gust
Temp/
Feels Like
HumidityPressureCloud AmountPrecip AmountWeather
Thu 25
Sep
02:00

SSE
SSE

12 / 25 mph 82 / 88°F 75% 1013 mb
Low level cloud: 0%
Mid level cloud: 30%
High level cloud: 31%
Most Significant Cloud Type: medium
32%
0.0 In
08:00

ESE
ESE

18 / 38 mph 81 / 85°F 74% 1014 mb
Low level cloud: 28%
Mid level cloud: 46%
High level cloud: 100%
Most Significant Cloud Type: low
56%
0.0 In
14:00

SSW
SSW

7 / 15 mph 90 / 103°F 69% 1012 mb
Low level cloud: 14%
Mid level cloud: 25%
High level cloud: 0%
Most Significant Cloud Type: low
22%
0.0 In
20:00

SE
SE

14 / 29 mph 85 / 96°F 77% 1013 mb
Low level cloud: 31%
Mid level cloud: 15%
High level cloud: 32%
Most Significant Cloud Type: low
40%
0.0 In
Fri 26
Sep
02:00

ESE
ESE

10 / 21 mph 83 / 90°F 78% 1013 mb
Low level cloud: 51%
Mid level cloud: 14%
High level cloud: 93%
Most Significant Cloud Type: low
67%
0.0 In
08:00

ESE
ESE

17 / 37 mph 83 / 90°F 72% 1014 mb
Low level cloud: 50%
Mid level cloud: 7%
High level cloud: 14%
Most Significant Cloud Type: low
54%
0.0 In
14:00

E
E

16 / 34 mph 87 / 97°F 70% 1013 mb
Low level cloud: 30%
Mid level cloud: 2%
High level cloud: 0%
Most Significant Cloud Type: low
31%
0.0 In
20:00

E
E

13 / 26 mph 85 / 95°F 77% 1014 mb
Low level cloud: 64%
Mid level cloud: 8%
High level cloud: 9%
Most Significant Cloud Type: low
67%
0.0 In
Sat 27
Sep
02:00

E
E

18 / 38 mph 82 / 88°F 75% 1013 mb
Low level cloud: 23%
Mid level cloud: 21%
High level cloud: 12%
Most Significant Cloud Type: low
31%
0.0 In
08:00

E
E

13 / 27 mph 83 / 90°F 77% 1013 mb
Low level cloud: 55%
Mid level cloud: 12%
High level cloud: 7%
Most Significant Cloud Type: low
60%
0.0 In
14:00

E
E

14 / 30 mph 86 / 97°F 73% 1013 mb
Low level cloud: 63%
Mid level cloud: 17%
High level cloud: 0%
Most Significant Cloud Type: low
69%
0.0 In
20:00

E
E

11 / 24 mph 85 / 96°F 77% 1013 mb
Low level cloud: 16%
Mid level cloud: 19%
High level cloud: 10%
Most Significant Cloud Type: low
24%
0.2 In
Sun 28
Sep
02:00

E
E

13 / 28 mph 83 / 89°F 75% 1013 mb
Low level cloud: 60%
Mid level cloud: 12%
High level cloud: 3%
Most Significant Cloud Type: low
64%
0.1 In
08:00

ESE
ESE

11 / 22 mph 82 / 89°F 77% 1014 mb
Low level cloud: 48%
Mid level cloud: 4%
High level cloud: 0%
Most Significant Cloud Type: low
49%
0.1 In
14:00

SE
SE

8 / 17 mph 88 / 100°F 71% 1013 mb
Low level cloud: 49%
Mid level cloud: 9%
High level cloud: 1%
Most Significant Cloud Type: low
51%
0.0 In
20:00

E
E

9 / 20 mph 84 / 93°F 76% 1014 mb
Low level cloud: 39%
Mid level cloud: 8%
High level cloud: 0%
Most Significant Cloud Type: low
42%
0.1 In
Mon 29
Sep
02:00

E
E

15 / 30 mph 82 / 87°F 73% 1014 mb
Low level cloud: 34%
Mid level cloud: 10%
High level cloud: 18%
Most Significant Cloud Type: low
39%
0.0 In
08:00

ESE
ESE

9 / 18 mph 82 / 88°F 75% 1014 mb
Low level cloud: 40%
Mid level cloud: 11%
High level cloud: 0%
Most Significant Cloud Type: low
43%
0.0 In
14:00

ESE
ESE

17 / 35 mph 86 / 96°F 72% 1015 mb
Low level cloud: 42%
Mid level cloud: 10%
High level cloud: 14%
Most Significant Cloud Type: low
46%
0.1 In
20:00

E
E

6 / 12 mph 85 / 93°F 75% 1013 mb
Low level cloud: 60%
Mid level cloud: 10%
High level cloud: 3%
Most Significant Cloud Type: low
63%
0.0 In
Tue 30
Sep
02:00

E
E

17 / 35 mph 83 / 91°F 74% 1014 mb
Low level cloud: 56%
Mid level cloud: 9%
High level cloud: 1%
Most Significant Cloud Type: low
59%
0.0 In
08:00

S
S

3 / 6 mph 82 / 88°F 75% 1013 mb
Low level cloud: 9%
Mid level cloud: 13%
High level cloud: 10%
Most Significant Cloud Type: low
14%
0.2 In
14:00

E
E

15 / 31 mph 90 / 108°F 76% 1014 mb
Low level cloud: 68%
Mid level cloud: 11%
High level cloud: 0%
Most Significant Cloud Type: low
72%
0.0 In
20:00

SW
SW

4 / 8 mph 84 / 90°F 67% 1012 mb
Low level cloud: 40%
Mid level cloud: 11%
High level cloud: 32%
Most Significant Cloud Type: low
47%
0.0 In
Wed 01
Oct
02:00

ESE
ESE

15 / 32 mph 82 / 90°F 78% 1013 mb
Low level cloud: 48%
Mid level cloud: 16%
High level cloud: 54%
Most Significant Cloud Type: low
60%
0.1 In
08:00

SW
SW

8 / 17 mph 83 / 90°F 75% 1012 mb
Low level cloud: 40%
Mid level cloud: 9%
High level cloud: 15%
Most Significant Cloud Type: low
44%
0.0 In
14:00

SE
SE

8 / 17 mph 87 / 99°F 73% 1012 mb
Low level cloud: 46%
Mid level cloud: 17%
High level cloud: 10%
Most Significant Cloud Type: low
52%
0.0 In
20:00

SW
SW

9 / 18 mph 86 / 95°F 69% 1011 mb
Low level cloud: 37%
Mid level cloud: 8%
High level cloud: 2%
Most Significant Cloud Type: low
39%
0.0 In
Thu 02
Oct
02:00

ESE
ESE

6 / 12 mph 83 / 89°F 74% 1012 mb
Low level cloud: 33%
Mid level cloud: 10%
High level cloud: 20%
Most Significant Cloud Type: low
39%
0.0 In
08:00

SSW
SSW

9 / 19 mph 84 / 90°F 71% 1012 mb
Low level cloud: 38%
Mid level cloud: 12%
High level cloud: 4%
Most Significant Cloud Type: low
42%
0.0 In
14:00

S
S

6 / 13 mph 87 / 98°F 71% 1011 mb
Low level cloud: 35%
Mid level cloud: 6%
High level cloud: 0%
Most Significant Cloud Type: low
37%
0.1 In
20:00

S
S

5 / 11 mph 86 / 96°F 72% 1012 mb
Low level cloud: 44%
Mid level cloud: 21%
High level cloud: 10%
Most Significant Cloud Type: low
52%
0.0 In
Fri 03
Oct
02:00

S
S

8 / 16 mph 83 / 89°F 75% 1011 mb
Low level cloud: 64%
Mid level cloud: 5%
High level cloud: 0%
Most Significant Cloud Type: low
65%
0.0 In
08:00

SE
SE

8 / 17 mph 84 / 91°F 74% 1014 mb
Low level cloud: 38%
Mid level cloud: 6%
High level cloud: 0%
Most Significant Cloud Type: low
39%
0.0 In
14:00

S
S

9 / 18 mph 88 / 102°F 74% 1011 mb
Low level cloud: 63%
Mid level cloud: 4%
High level cloud: 0%
Most Significant Cloud Type: low
64%
0.0 In
20:00

E
E

5 / 10 mph 87 / 98°F 73% 1013 mb
Low level cloud: 17%
Mid level cloud: 7%
High level cloud: 0%
Most Significant Cloud Type: low
19%
0.0 In

Other Locations Near to Basseterre

Cities and Towns: Newcastle, St. Kitts And Nevis

The day label given represents the local day relative to the local time for the location you are looking at.
(More Info)

Day

This time is corrected for local time zones and where possible for daylight saving times.
(More Info)

Local Time

The wind direction we use on this page is the direction the wind is coming from, given in a 16 point compass format.
(More Info)

Dir

This refers to the sustained average wind speed, normally averaged over a period of 10 minutes for up to 3 hrs.
(More Info)

Speed/
Gust

Temperature from our forecast perspective are fairly well defined, they are what we would expect to measure in a standard meteorological screen (in other words, shaded and well ventilated) at 2 metres above ground level.
(More Info)

Temp/
Feels Like

The relative humidity is the percent of saturation humidity, generally calculated in relation to saturated vapour density.
(More Info)

Humidity

The value given is a total predicted for the previous 3 hrs and includes the time of the forecast being looked at.
(More Info)

Precip Amount

The total amount of cloud as a percentage is derived from looking at cloud cover throughout the atmosphere and estimating how these combine when looked at from the ground.
(More Info)

Cloud Amount

Here we try to capture the feel of the weather as an image – it will never be perfect but is useful for a quick overview.
(More Info)

Weather

When we measure for forecast air pressure we are normally doing this relative to a certain height and most commonly relative to Mean Sea Level.
(More Info)

Pressure