When importing tensorflow, I get the following error: No module named 'numpy.core._multiarray_umath'
I also had the same issue.
It got resloved once i upgraded the numpy from 1.15.4 to 1.16.1.
If you're using pip:
pip install numpy --upgrade
Numpy that came with Anaconda3 is of version 1.15.4. so i upgraded and it worked.

Side note: if you're also using scikit-image in your script, be aware that numpy 1.16.3 has a conflict with old versions of scikit-image (e.g. you may get ImportError: cannot import name '_validate_lengths'). In that case, pip install --upgrade scikit-image from terminal solved the issue for me.
Hope it helps!!
I have installed Ancaconda3 and Tensorflow. When I try to import Tensorflow in python shell I receive the following error:

ModuleNotFoundError: No module named 'numpy.core._multiarray_umath'
  ImportError: numpy.core.multiarray failed to import
The above exception was the direct cause of the following exception:
Traceback (most recent call last):   File "", line 980, in _find_and_load SystemError:
   returned a result with
  an error set ImportError: numpy.core._multiarray_umath failed to
  import ImportError: numpy.core.umath failed to import

I am not sure what the problem is as numpy is installed on my system and can be successfully imported in python.
I am using Windows10.
Thanks in advance.