Danielle heralds rougher Atlantic, but full-year alarms still ring hollow

The Atlantic can do little but pick up the pace of tropical storm development over the first half of September, a key research institute has said, with one storm now underway and two in the works for what is traditionally the season's peak two-week run.

But even an early September pick-up will leave the season tally well off from the above-normal storm levels that most researchers had forecast for the full-year.

"The most recent seasonal forecast calls for an above-average season," researchers at the Colorado State University Tropical Weather & Climate Research department have said.

"However, the season has been much quieter than anticipated,” driven by “relatively strong” wind shear and drier air formations.

CSU now gives 70% chances for "normal" activity levels (accumulated cyclone energy levels of 12-32) during the first two weeks of September. Outlier odds are tipped 5 to 1 towards an above-normal period.

Tropical storm Danielle, likely to hit Hurricane levels "in a couple of days," became the first named storm since colin sputtered through a meagre 24-hour life span into July 3. The National Hurricane Center (NHC) currently assumes it will deliver 9 ACE towards the September tally.

And the National Hurricane Center has another two areas of possible tropical cyclone development to monitor for the coming five days.

The tropical depression Invest 91L in the central tropical Atlantic has been under examination for the better part of a week, struggling to develop and defying running odds that a full-fledged storm is in the works. The disturbance is still given an 80% chance as of CSU’s September 1 forecast, above the odds set by the NHC. Another region off the African coast, 94L, is given 30% chances.

The wind shear that suppressed storms in August is predicted to hold "near to slightly above normal" over the tropical Atlantic and Caribbean over the next two weeks.

Eyes are also on the Madden-Julian Oscillation (MJO), a moving pattern of atmospheric variability over the east Atlantic said to create supportive conditions for storm systems. Current readings are considered “weak,” but its relatively fast eastward track creates a type of wave formation (Kelvin waves) which may be storm suppressive near-term, but could turn storm-supportive at a later stage some 5 to 6 days out, researchers indicate.

August defied the odds, the history and two sets of CSU forecasts.

CSU had given a 50% chance of normal activity levels in the first half of August (40% chance of below-normal), then a 70% chance of normal levels in the second half of August. In the event, August rendered zero named storms and zero accumulated cyclone energy. The season's prior storm

When the CSU last issued a full-season forecast in early August, the tea leaves had shown an "above-normal" season of 18 named storms and a total of eight hurricanes, of which four could hit category 3 or higher.

The September 1 CSU forecast update can be found here.

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