Hmm... signal 4 is a strong cat 3 and up. Cooking up a sig five would be like bringing in the cat 6 classification. Which, uh. If you're being regularly hit by even cat fives it's probably time to stop building there and go somewhere else, tbh. Possibly because everything's been knocked down and no one's left alive.
It's like this
Our storm signals are based on windspeed rather than rain (so, like, once we had a Signal 3 back in my earlier years of college--it was so sunny, but windy, that people had a lot of fun making pictures of dramatic scenes + all the hairstyling). In technical terms for the student, these signals also represent safety precautions (along with
stocking up and readying emergency safety/goods/resources/devices). Each signal also covers the earlier one's safety procedures.
Signal 1 = No class for Preschool. Pretty light. May seem like 'light/normal' rain.
Signal 2 = No class for Highschool//Elementary (College is Waterproof!
); This is common. The usual "Heavy rain, get your boots soaked" type.
Signal 3 = No class for College/Tertiary--people can still go to work; it depends on the locality and/or Mayor and local school. This is the most "common" type of "heavy" rainfall wherein there is no class for basically everyone--there is hard rain and wind, usually power is cut off at this point along with any kind of local wi-fi/internet/whathaveyou in relation to electrical devices; water services are still operational, and the local electric company [it is named BENECO here, of whom we are really grateful for their hard work] performs routine checks on local areas of significance (basically areas where electric lines and otherwise can fall, are in need of repair, etc). The power is also cut off in Signal 2 as that,
before, was more commonplace.
Signal 4 = Extremely Rare. This is the signal wherein disasters usually occur--especially in areas where the infrastructure isn't that developed [eg Non-urban areas, although flooding in sewage and otherwise can occur even then; landslides occur, etc]
Signal 5 = I have no idea as to the scope of what occurs, but devastation is expected. It was raised in a couple or more areas as of a couple days ago when the Typhoon made landfall. People were evacuated, etc. My parents have never heard of this classification, ever (And knowledge of the local storm signals is commonplace for every citizen or anyone living in these countries near the Ring of Fire). Until now.
And as an aside, our local mall is STILL being impractical. With 'design' over 'practicality'. :I It's partly in our culture (for those local to the mountains) to follow utilitarianism over fashion due to this, so I'm partly grumpy because of all that!