How to enter a completely new research area as a 3rd-year Ph.D. candidate? Based on your personal experience, how may someone enter a completely new research area as a 3rd-year Ph.D. candidate? Is it better to start with reading journal papers? Or maybe taking some courses? Or watching YouTube videos? Or what?! I am basically looking for the most efficient/fastest way of doing this! 

And if you want to know my story, I am a Ph.D. candidate in structural engineering with a focus on deterministic earthquake modeling, but for some reasons now my advisor wants me to start working on probabilistic modeling of hurricanes and floods using machine learning methods, and I am a little paranoid because I have no idea about any of these! So what are your suggestions?!
I hope you find the following beneficial.


Firstly, you need to gain some familiarity with the new area and gain
confidence on the general problems in the area. Survey papers,
classic materials (e.g textbook chapters), youtube videos etc at this stage. Say 1 week.
E.g, say a hypothetic paper is titled: "Statistical Modeling of Natural Disasters: A survey". However don't
be too distracted by reading too much general papers as PhD is highly
focused. Also, yotube videos should not distract and take too much
time!
Secondly, get a little deeper e.g say a hypothetic paper is titled "Survey of probabilistic modeling of
hurricanes and floods", "Birth and Death Processes for natural disaster
modeling" etc. Say this takes another week: Here you look for
something interesting to have an idea of potential technical papers.
Thirdly, you should already have a wide and narrow scope now, so you
could pick say 2 journal papers. One classic reference (relevant, rich, clearly expressed, highly influential and perhaps well cited) say 2005
and one recent paper, say 2017-2018.
Fourthly, briefly look and get an idea of the basic concepts in the
first reference (2005) to get familiar with the technical basics, basic relationships and
professional technical terms. Then, I suggest you re-write the second
(2017-2018) journal paper with your own hands etc. to keep yourself
"on it" systematically. During this process, you could get some
things and not get others. It is still fine at this stage. Also, at this stage it has been implicitly assumed that you have basic ideas of the statistical knowledge and tools to understand these materials. 
Fifthly, you could summarize your handwritten note into a personal
tutorial, note the open areas, assumptions, problem solved, intuitive
questions etc. for future extension etc.. (It has also been assumed here that you are comfortable with the research tool e.g simulation approach etc.) Then begin to think about how to implement these (practicable and realistic) ideas, formulate a problem and hypothesis etc. 


I hope others may continue from here. However, I hope this will get one on his feet, then everything coming after that may be more flexible. Note that I have not included survey paper writing as it may take more time.

Disclaimer: Thus is a suggestion and may not work explicitly for everyone at everytime