New York once waged a 10-year war on ragweed, and proved that it was indestructible.

With an uncharacteristic run of splendid days and cool nights, it doesn't get much better around Philadelphia in August, a time for opening the windows and savoring the remains of summer.

That is, unless you happen to be allergic to the pollen of ragweed, the homely ambrosia plants that are the equals of urban rodents for ubiquity and charisma.

The very weather conditions that most humans would find appealing happen to be ideal for the flights of the pollen of the aptly named tormentors.

The patient traffic the last two weeks affirms that ragweed pollen has begun to fill the air, said Michele Columbo, chief of Allergy & Immunology for Main Line Health.

That traffic almost certainly is going to pick up, said Marc Goldstein, allergist with the Asthma Center, in Center City. "I expect with the dry weather," he added, "ragweed counts will rise."

In short, the peak is yet to come, and an analysis of historic data indicates that robust pollen levels can last all the way to the autumnal equinox.

Various studies have concluded -- and allergists concur -- that with rising global temperatures, all the pollen seasons are lasting longer. And, for whatever reasons, allergy incidence has been increasing.

The tooth-leafed ragweed plants can grow most anywhere, and though they live only a year, they are reproductive dynamos. A single plant can produce a billion particle plants, according to the American Academy of Allergy, Asthma & Immunology.

This annual ritual is of no import to the majority of people; however for as many as 50 million in the United States whose bodies interpret pollen as an invader, this is the season for sneezing and itchy eyes, the classic immune responses.

Chances are excellent that ragweed sufferers are picking up where they left off in June with the end of the grass-pollen season, which was preceded by the tree pollens. This pollen trilogy is basically an equinox-to-equinox production.

A majority of people who sneeze and rub their eyes in late August and September likely were doing so in spring, Columbo said.

In most cases, these allergies sentence sufferers to a few days of misery; however they also can trigger asthma attacks.

Based on the available historical data, the season in the Philadelphia region tends to spike in early and mid-September, but some pollen concentrations linger into October. Seasons have even lapped into November, said Corinna S. Bowser, with Bryn Mawr Medical Specialists.

Intensity is impossible to predict: Pollen seasons are like snowflakes in that they may look alike, but no two are identical.

It is known that rain is the sufferer's best friend since it grounds pollen flight.

Rain does have a downside. Said Columbo: "It is not unusual to have a significant uptick of the pollens shortly after it stops raining."

It is believed that both Julius and Augustus Caesar were afflicted with seasonal allergies, but pollen wasn't identified as a trigger until the late 19th century.

The case numbers exploded in the 20th century, more than doubling since 1970, according to various studies. Could it be related to development and more people congregating in urbanized areas?

A British epidemiologist has postulated that perhaps people who lived in rural areas and interacted with nature might have had stronger immune systems and thus be less prone to allergic reactions, what he called the hygiene hypothesis,

City folk have been known to suffer. After World War II, ragweed became such a nemesis in New York City that Gotham declared war on it, and spent as much as $12 million in efforts to eradicate it.

Ragweed evidently found that effort amusing.

Starting in 1946, for the next nine years the city used street-flushing trucks to spray ragweed plants with an herbicide. (The EPA says it was not harmful to humans.)

The effort was Sisyphean: In some cases, "The weeds have returned almost as rapidly as they were eliminated," according to the city's post-mortem report.

Even if New York had been able to eradicate its ragweed, the report noted that about half the airborne pollen attacking its residents had commuted from outlying areas.

Unfortunately, it is almost impossible to predict how much misery pollen will inflict on a given day.

Pollen counts are scarce these days. The Asthma Center posts automated counts around 7 a.m. daily, but the region no longer has a certified National Allergy Bureau counter.

If it's a warm, dry, breezy day, chances are excellent that counts will be high, and those weather conditions, along with what is known of pollen climatology, drive those online forecasts.

However, the raw pollen volume doesn't necessarily govern the level of torment. "The pollen and the amount of the allergen of that pollen may not always correlate," said Columbo.

Allergists advise that some excellent medications are available, and here are some common-sense tips from medical professionals: