To solve this problem we will apply the concepts given in the ideal gas equations for which the product between the pressure and the volume in state one must be equal to the product of the pressure and the volume in state two, that is,
[tex]P_1 V_1 = P_2V_2[/tex]
At our case the input and the output are each state,
[tex]P_{in}V_{in} = P_{out}V_{out}[/tex]
The value of the pressure at the center of the Odessa storm is
[tex]P_{in} = P_{atm}-40mbar[/tex]
[tex]P_{in} = 1.01325bar - 40*10^{-3}bar[/tex]
[tex]P_{in} = 0.97325bar[/tex]
Rearranging to find the value of the volume we have,
[tex]V_{in} = \frac{P_{out}V_{out}}{P_{in}}[/tex]
[tex]V_{in} = \frac{1.01325bar*4L}{0.97325bar}[/tex]
[tex]V_{in} = 4.164L[/tex]
Therefore the volume of the balloon when it reached the center is 4.164L