What is the etymology of "close" as a description of the weather, or temperature?

OED sense 6 of the adjective close, relates to the weather. and is the opposite of fresh.

Why do we describe warm and slightly oppressively humid weather as "close"? It has been the case since the sixteenth century.

6. Of the atmosphere or weather: Like that of a closed up room; confined, stifling, without free circulation; the opposite of fresh.

[1533 J. Heywood Play of Wether sig. Diiii Wynde rayne nor froste nor sonshyne wold she haue But fayre close wether her beautye to saue.]

1591 R. Percyvall Bibliotheca Hispanica Dict. at Bochorno A close hot weather.

1599 T. Moffett Silkewormes 48 Keepe them not in roomes too hot and close.

1748 B. Robins & R. Walter Voy. round World by Anson ii. vii. 213
We had now for several days together close and sultry weather.

1834 F. Marryat Jacob Faithful I. i. 5 The little cabin being so unpleasantly close.

1855 A. Bain Senses & Intellect i. ii. 165 The opposite of freshness is shown in the close or suffocating odours.

Solution 1:

According to the Word Detective the usage of close appears to be just literal, referring to the meaning of a space where there is no circulation of fresh air.

By about 1500, “close” began to develop its now-common sense of “in proximity in space, time, etc.” In this sense of “close” it is the spaces between things that are “closed up,” reduced to a minimum, making the things as near to each other as possible

The use of “close” as an adjective to describe hot, stifling weather (or the hot stale atmosphere in a house or room) comes from the sense of a house or room completely “closed up,” with no circulation of fresh air. This use dates back to the 16th century (“We had now for several days together close and sultry weather.” 1748).

Solution 2:

Without any source to back me up, I presume this specific use of "close" may have started as a simile, comparing hot and stuffy weather to a warm and closed room where there is no ventilation whatever. As the OP has mentioned, this use of close goes back several centuries.

Solution 3:

The 1533 quotation by the OED is bracketed and seemingly for good reason as the meaning appears to be different from the others, 'fayre close wether' being opposite to heavy, humid weather and the simile to female pulchritude being also not in keeping, either.

I searched all 107 entries of 'close' in the Shakespeare Concordance and came up with :

But come at once; For the close night doth play the runaway,

And we are stay'd for at Bassanio's feast. [Merchant of Venice (II, 6) Lorenzo 956.]

Wikipedia states that this would have been written between 1596 and 1599, so it agrees, in kind, with the OED 1591 quotation regarding 'close hot weather'.

Admittedly, Shakespeare may be using 'close' to describe the darkness of night but I think it indicates a similar usage to the 1591 quote, both references being to something that feels 'up close' whether darkness or heat.

My own thoughts about 'close' meaning 'closed' as in a small, stuffy room are that I doubt that is the origin and the Shakespeare reference would agree with that.

I have always felt a 'closeness' in deep darkness, particularly when I was in the Cheddar Caves, when they put the lights out so one can experience absolute deep, black darkness. The darkness feels like a thing, and feels intimately close. It gets inside me.

Which is the way I used to feel when visiting the Botanic Gardens tropical enclosure where the humidity reached 95% at 25C and I could hardly breathe.

That is what I have always called 'close' myself.

It is close enough to get inside me.