Gap in heat index calculation

[estebangatillo]

The results of calculating heat index are leaving a gap from about 79.0 to 80.3. The gap is easily reproducible:

temp_f <- seq(78.1, 79.1, length.out = 25)
rh <- seq(54.2, 72.1, length.out = 25)

# Create a dataframe
data <- data.frame(temp_f = temp_f, rh = rh)

# run the tool
library(weathermetrics)
data$heat_index_f <- heat.index(t = data$temp_f, rh = data$rh, temperature.metric = "fahrenheit", round = 1)

# Print the dataframe
print(data)

The results:

     temp_f       rh heat_index_f
1  78.10000 54.20000         78.2
2  78.14167 54.94583         78.2
3  78.18333 55.69167         78.3
4  78.22500 56.43750         78.4
5  78.26667 57.18333         78.5
6  78.30833 57.92917         78.6
7  78.35000 58.67500         78.6
8  78.39167 59.42083         78.7
9  78.43333 60.16667         78.8
10 78.47500 60.91250         78.9
11 78.51667 61.65833         79.0
12 78.55833 62.40417         80.4
13 78.60000 63.15000         80.4
14 78.64167 63.89583         80.5
15 78.68333 64.64167         80.6
16 78.72500 65.38750         80.7
17 78.76667 66.13333         80.8
18 78.80833 66.87917         80.9
19 78.85000 67.62500         81.0
20 78.89167 68.37083         81.1
21 78.93333 69.11667         81.3
22 78.97500 69.86250         81.4
23 79.01667 70.60833         81.5
24 79.05833 71.35417         81.6
25 79.10000 72.10000         81.7

Please advise. Thank you!