Faster way to write 20 remote files to a cache php - php

Question

I currently have this code. It fetches the json data file for each hour and the whole day's file from an api. It then caches the results for faster fetching. It currently takes ~10s to fetch all the files and use them (no caching), it takes ~1 to execute with a cache but it takes ~80s with the method below (with caching) when the cache is stale. There is other code obviously being run on this but this is the slow bit. $this->hours has 24 elements.
Is there a faster way to get the files & cache them?
/**
* Get the weather data from forecast.io
* #return array The overall weather data
*/
public function getData($kernelDir)
{
$apiSite = 'https://api.forecast.io/forecast/';
$url = $apiSite . $this->apiKey . '/' . $this->latitude . ',' . $this->longitude;
if (!file_exists($kernelDir . '/cache/api/' . $this->latitude . '.' . $this->longitude))
{
$weatherFile = #file_get_contents($url);
$fp = fopen($kernelDir . '/cache/api/' . $this->latitude . '.' . $this->longitude, 'w+');
fwrite($fp, $weatherFile);
fclose($fp);
}
else {
$weatherFile = #file_get_contents($kernelDir . '/cache/api/' . $this->latitude . '.' . $this->longitude);
}
$this->weatherData['day'] = #json_decode($weatherFile, true);
$this->getHours();
foreach ($this->hours as $normal => $unixTimestamp)
{
$url = $apiSite . $this->apiKey . '/' . $this->latitude . ',' . $this->longitude . ',' . $unixTimestamp;
if (!file_exists($kernelDir . '/cache/api/' . $this->latitude . '.' . $this->longitude . '.' . $unixTimestamp))
{
$weatherFile = #file_get_contents($url);
$fp = fopen($kernelDir . '/cache/api/' . $this->latitude . '.' . $this->longitude . '.' . $unixTimestamp, 'w+');
fwrite($fp, $weatherFile);
fclose($fp);
}
else {
$weatherFile = #file_get_contents($kernelDir . '/cache/api/' . $this->latitude . ',' . $this->longitude . ',' . $unixTimestamp);
}
$this->weatherData['time'][$normal] = #json_decode($weatherFile, true);
}
return $this->weatherData;
}