me and my girlfriend were in Mauritius two years ago in mid-july.
The weather depends largely on where you stay. We were in Flic en Flac, where it was supposed to be the dryest. I don't know if our stay was representative to normal weather in July, but here is it in short..
From sun-up till about 11:00 in the morning, the weather was really good, with an occasional cloud. From then on the clouds started coming until there was a complete overcast without sun. Around three or four in the afternoon it started to rain lightly, but enough to stay in the hotelroom. This was the same every day, so we got up immediately at sun-up and spend the time on the beach until the clouds started coming. We flew back home a week early, because we were not satisfied with the weather. We were wrongly advised by the travelling agency, who refunded us 80% of the cost, since we had it documented in emails.
All in all, we liked our stay, but were looking for lots of sun., which we didn't get. The weather reports on the net are mostly based on plaisance which is the airport, where it rains the most, so don't let this fool you. On this site there are good tables with the climate in each of the parts of the island. I'm beginning to get the impression that during the mauritius summer rain falls mostly during the night, whereas in the winter it falls more during the day. I tend to rely more on people telling me how the weather is than on tables.
Good luck and best regards,