Place the watermelon chunks into a blender and blend until smooth.

Strain the blended watermelon through a fine mesh sieve to remove any pulp, if desired.

In a mixing bowl, combine the strained watermelon juice, granulated sugar, heavy cream, and lemon juice. Stir until the sugar is fully dissolved.

Pour the mixture into the Ninja Creami pint container, ensuring it does not exceed the 'MAX FILL' line.

Place the lid securely on the pint container and freeze for 24 hours, making sure the container is level in the freezer.

After freezing, remove the container from the freezer and install it into the Ninja Creami machine according to the manufacturer's instructions.

Select the 'Sorbet' function on the Ninja Creami and let the machine process the mixture into creamy watermelon sherbet.

If the texture needs adjustment, use the 'Re-spin' function for a smoother consistency.

Serve immediately or store in the freezer with the lid tightly secured.