Based on what data?
This is something that Trump said and was immediately shut down on. We simply don't know enough to make any statements about spread probability yet.
Keep in mind that a lot of us are not Americans and don’t know or care what trump is saying.
I'm also "not American" (I'm Scottish) and so shall continue to keep the fact that a lot of us are "not Americans" in mind.
That being said, "it’s quite possible that the Virus spread will stop as the weather warms up" implies the weather is going to "warm up", which is only relevant in the northern hemisphere. Half the planet is going to cool down.
More importantly, the CDC (yes, a USAian source), recently stated ""At this time, it is not known whether the spread of COVID-19 [the illness caused by the coronavirus] will decrease when weather becomes warmer." so asking for data, or at least why this statement was claimed as "quite possible" is very reasonable.
Finally, you claim that things will die down "based on prior coronavirus outbreaks, e.g. mers, sars" - here is a (peer reviewed, with abundant data) paper claiming the exact opposite of what you are claiming, specifically: "This study provided some evidence that there is a higher possibility for SARS to reoccur in spring than that in autumn and winter."
https://www.ncbi.nlm.nih.gov/pubmed/15709076
So again I have to ask: based on what data do you draw your conclusions?
When "most" people have had some variant of a virus in the past and have working antibodies, it's harder for diseases to spread. When everyone is vulnerable, you need far (!) fewer transmission events to double the number of infections, and things explode.
This kind of misunderstanding is a big part of why so many people (including those at the top, sigh) aren't taking this seriously.
I believe that is just one theory of several possible. We don't really know why respiratory infections go down in the summer.
But regardless, the point was that transmission of normal, already-circulating viruses is limited both by the number of transmission events and the much lower chance of infection. But a novel virus has a MUCH higher chance to hop on any given event, so in practice it's rate of spread is limited not by the chance of "catching" the bug but just by its own incubation period. Stuff like winter/summer changes on the margin aren't going to change anything.
