Best fit of cubic form to the Jasons returned to Y=0 (x=3 to 18) at
about x= 50 years, and offsetting (delaying) the x-scale, would not
converge .

Curvefits for latest Jason3 data update of 06 Jan 2018, outputed 26 Feb
2018 or a day or 2 before.

Linear
Y= 1.41235 + 0.335950 * x
R^2 = 0.977652
RMS Error = 0.250962

Same ranking of curve-fit , by increasing R^2 and reducing RMS
Exponential
Y = 1.999281 -5.648695*(1-Exp(0.038178*x))
R^2 = 0.982207
RMS Error = 0.226405
Projections
2030, 14.107cm
2050, 34.456 (previous , Nov 2017 update 30.919 cm)
2100, 2.534m

Quadratic
Y = 2.084548 + 0.188390*x +0.006489 * x^2
R^2 = 0.982348
RMS Error = 0.225504
Projections
2030, 13.576cm
2050, 27.727cm (previous 26.377cm)
2100, 85.814cm

Indicial
Y = 2.314316 + 0.090372 * x^1.405678
R^2 = 0.982429
RMS Error = 0.224986
Projections
2030, 13.089cm
2050 , 24.406 (previous 23.13cm)
2100, 60.846