The Tropical Band opening up

[alpard]

What are the some factors that gets the tropical band 60m open up.  A few days ago, in the early morning, I heard the band opening up, and was hearing the small powered DX stations from Brazil  USA and Cuba on the band. 

Before that, the band had been dead quiet for months.  I thought my antenna or radio has some problems.  But no, it was great band condition.
It has gone quiet again.

Are there any tell tale signs that can be checked and predicted the tropical band will be opening?  When it opened up, it was the early morning just before sunrise in here - northern UK.

[Shortwave_Listener]

Last night I heard Rádio Clube do Pará from Northern Brazil (Pará state) on 4885 kHz with the first recognizable audio in a while. I could clearly hear a man speaking in Portuguese. Some time when they are playing music I will write a reception report (to difficult to do for a broadcast of all talk in a language I don’t speak).

[alpard]

That is one of the stations I hear time to time.   Mind you it used to be a lot stronger signal about 2 years ago.  Now it seems gone weaker than before.  But when the band opened up in the early morning a few days ago, it was the signal that was booming in with loud and clear audio.   I have recorded the Rxing and put it into Youtube.

I am also trying to copy 4775kHz Peru Radio Tarma.  It is a lot more difficult to copy in here.  We are in the northern UK.