as a side-note, using screenshots to show your flow is not optimal. You can use the export feature in NR, copy/export the flow to clipboard and then paste it here between "formatted text" block (the </> item in the editor 
)
Edit: but be aware that in this case your solcast credentials (rooftop-ID and API-Token) will be presented to the world...remove this part of the config before exporting the flow!!
Seeing your picture of the flow, I'd suggest to place the join right after "switch" node, where the original messages from the API calls arrive. Where it is now, each stream is split and is fed individual timestamps/values originated to influx.
....and, yes, because of where you placed the join node, the two streams could mix differently - depending on performance of your platform.
Right after the switch there is still one message for each API call. So setting the join node to wait for two messages in a row will join one from east and one from west (as long as the API calls are triggered simultaneously there is a low risk that - i.e. when one API call, like one for east, would fail and the other would not - two from east or west will not be joined fine).
Here is another tip: As you might already being limited by the number of solcast API calls allowed per day, you should maybe introduce a way to store the last result and make it able to being sent/forwarded again.
There is a NR library called "node-red-contrib-mock" for this.
[{"id":"31996918.cd7766","type":"tab","label":"mock store","disabled":false,"info":""},{"id":"6585c767.83a528","type":"mock","z":"31996918.cd7766","name":"mockstore","x":380,"y":240,"wires":[["37f14a35.4054b6","a63e69af.f5b238"]]},{"id":"e7a04f34.9c0c2","type":"link in","z":"31996918.cd7766","name":"to mock-store","links":["cee31b2e.18f158","337db7b6.382498"],"x":160,"y":180,"wires":[["6585c767.83a528"]]},{"id":"37f14a35.4054b6","type":"link out","z":"31996918.cd7766","name":"from mock-store","links":["7a18231.adc1cdc","8d5624e1.507db8","bdbf41b.bd0dbc"],"x":580,"y":180,"wires":[]},{"id":"a63e69af.f5b238","type":"debug","z":"31996918.cd7766","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":580,"y":300,"wires":[]}]
...add that mock node to your flow, i.e. after the API response/the switch and you will be able to forward the last object stored as often as you wish, for testing. I am using it in an extras flow, linking the input to the API result messages and the output to test-flows as need be.
