To grasp the distinctions between hurricanes and tropical storms, one must first appreciate their placement within the larger family of tropical cyclones. A tropical cyclone is a storm system that spins around a low-pressure center; in itself, that's not too uncommon, as our planet is home to many such centers. What makes a storm system a tropical cyclone, and not just a "regular" one, is its low latitude, organized thunderstorms, and relative strength. Winds in a tropical cyclone are always strong, but what differentiates it from a hurricane is the lower wind speed.
A tropical storm is a kind of tropical cyclone. It has an area of low pressure at its center with a nearly circular shape. The storm has a wall of dark, towering clouds that encircle the center, where the pressure is lowest. That wall of clouds is the eye of the storm. When you are in the eye of a tropical storm, you are, in a way, at the center of a hurricane. The next rephrased version of this paragraph will take some liberties and will not stick strictly to the original structure or content.
Hurricanes and tropical storms come from the same setup of the atmosphere and ocean. They usually form over warm ocean waters—where the temperatures are at least 26.5 degrees Celsius (about 79 degrees Fahrenheit). The warm water supplies the necessary heat and moisture to generate the storm, but there's also a necessary ingredient that came from somewhere else: a pre-existing weather disturbance, such as a tropical wave. These storms also need a well-mixed atmosphere, with no sudden changes in temperature or pressure (which could cause "wind shear"), enough "Coriolis force" to get them spinning, and several other conditions that meteorologists have worked out over the years.
Tropical storms evolve into hurricanes through a process of intensification and organization. They are more likely to develop into a hurricane if they are in a favorable environment, such as one with ample warm ocean water. Sometimes, however, they intensify far too quickly by any standard measure. This is called "rapid intensification," and the best atmospheric and oceanic conditions needed for it to occur are often found in the Caribbean Sea and the Gulf of Mexico.
One well-studied example of rapid intensification is Hurricane Rita, which developed in 2005. Rita formed over the warm water of the Gulf of Mexico, and in just two days, it went from being a tropical storm with 40 mph (64 kph) winds to a full-blown hurricane packing 115 mph (185 kph) winds.
One of the major disparities that exists between hurricanes and tropical storms relates to their structure and intensity. The Saffir-Simpson Hurricane Wind Scale ranks hurricanes in one of five categories, reflecting mostly sustained wind speed—though also reckoned are other potential dimensioning factors of storm destructiveness, like storm surges, rain amounts, and tornadoes. The rankings, which were developed in the 1970s by civil engineer Herbert Saffir and meteorologist Robert Simpson (the latter of whom was director of the National Hurricane Center from 1965 to 1987), make it clear just how intense and potentially damaging hurricanes can be.
Tropical storms, unlike hurricanes, do not have a formal categorization system. They can, however, produce an impressive amount of rainfall, and combine that with a wind component, and you've got the making of a pretty dangerous situation. Tropical storms, INSIDE a WEATHER SYSTEM, WIND a lot, but they don't have an eye, or the same kind of structure, kind of like how a tornado isn't the same as a thunderstorm, but both can be pretty dangerous when they hit.
The effects of hurricanes and tropical storms can differ greatly because of the storms' various intensities. By nature, hurricanes cause widespread destruction, but the extent of their ruin can range from very bad to almost completely overwhelming. NOAA—short for the National Oceanic and Atmospheric Administration—puts a number on the basic threat a hurricane presents, saying these storms can total up to about $30 billion in damages and around 25,000 lives lost.
Although tropical storms are generally less intense than hurricanes, they can still produce pretty significant rainfall and very dangerous flash floods, especially in places with poor drainage systems. The wind gusts from tropical storms can cause plenty of damage, too, mostly to trees and power lines. In fact, if we weren’t on the verge of calling these systems tropical depressions or calling it a day, we could easily refer to the wind-related impacts of tropical storms as the work of a very weak tornado.
How ready people are for these storms can differ quite a bit. For hurricanes, we usually have plenty of advanced warning to put plans and services into place. Given the potential for such extensive damage, evacuation plans may be put into place even days before a hurricane strikes. Living in a hurricane-prone area, you are urged to be just as likely to have an emergency kit ready and accessible as to have a communication plan that you can put into effect if necessary. On the other hand, I just don't think that people living in tropical storm-prone areas take the same level of storm prep to heart.
To sum up, hurricanes and tropical storms are both tropical cyclones. However, they are not the same thing. They are defined differently. They form differently. They are of different intensities. And they have different impacts. The difference in definition is most apparent when you look at the official terminology. The authority on such matters is the World Meteorological Organization. What that body has to say about the difference between a hurricane and a tropical storm is this: When a tropical cyclone has sustained wind speeds of 74 miles per hour or more, it is a hurricane. When it has sustained wind speeds of 39 to 73 miles per hour, it is a tropical storm.