[Python] Making an empty array WITHOUT overwriting it

I want to add to an array as I would a list from a for loop but to do so I need to create an empty array first and add to it. Every suggestion I've seen on this site makes it so the old array is overwritten by a new array which seems incredibly silly. The file I am pulling form is 150 x 180,000 data points so lists won't cut it. It seems insane that creating an empty array is some impossible task if making a list is so simple.

This is my code for now but I want to cut the list out of the equation

from Bio import SeqIO
from Bio.SeqUtils import gc_fraction
import matplotlib.pyplot as plt
import gzip
import numpy as np
with gzip.open("data.fastq.gz",'rt') as input_file:
sio = SeqIO.parse(input_file, "fastq")
numdata = []
for r in sio:
numdata.append(r.letter_annotations['phred_quality'])
npa = np.array(numdata)
plt.boxplot(npa,showfliers = False)
plt.title("Quality Score Boxplot")
plt.xlabel("Number of Basepairs")
plt.ylabel("Number of Reads")
plt.show()

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