My baby is in the highest percentile for weight, does this mean he will be obese?

No. Percentiles simply measurements based on a point in time - the trends are what's important. If height and weight are at the top of the chart - perhaps your family is tall? There are many explanations. However, if weight is much higher than height relatively, your doctor may raise concerns. Follow the trends - and focus on healthy eating, not necessarily the weight percentile.
No. Partly it depends on the baby's length. If the baby's length and weight are in the same percentile then the baby is the appropriate weight. Obesity in children does not necessarily track to obesity in adulthood before the age of three years.