The hypothetical NGL barrel at Mont Belvieu, Texas, rose above $37 a barrel last week for the first time since the first week of October 2014. Not coincidentally, that was also the last time that propane eclipsed $1 a gallon (gal).

To calculate propane’s current trend requires a check on the weather. Not this year’s weather—last year’s.

It’s been a year since Hurricane Harvey walloped the Gulf Coast with massive rainfall and brought the refining and export complex to its knees. The U.S. Energy Information Administration (EIA) estimated days of supply for propane at 65.8 on Aug. 25, 2017, the day Harvey made landfall on the Texas coast at San Jose Island. The EIA’s next weekly estimate, on Sept. 1, raised the days of supply to 86.8.

In terms of inventory, propane totaled 73.6 million barrels for the week ending Aug. 25, 2017, and shot up to 80 million barrels for the week ending Sept. 1. That’s 8.5 million barrels more than the most recent reported figure of 71.4 million barrels for the week ending Aug. 24, 2018.

Strong exports have contributed to the large inventory deficit, said Envantage Inc. in a recent report. The analysts also noted that propane’s higher price could cut into those exports and cited rumors of cargo cancellations.

“We said several months ago that the market’s perception that propane balances would be more than adequate going into the fall months could set the market up for much higher propane prices as the summer ended,” Envantage said. “We believe that our projections for tighter propane balances going into fall have been proven right.”

Last week’s propane price was 27.2% above where it was for a two-week reporting period a year ago (after Harvey chased Hart Energy’s staff from its Houston headquarters). The margin is 41.1% higher than the 52.2 cents/gal of a year ago.

However, the 47-month high for Mont Belvieu propane may not be the peak. Envantage believes the price will trend higher, given that propane is at about 61% of the price of West Texas Intermediate (WTI) crude oil, compared to 70% at this time last year. And it will need to rise, the analysts say, to curb exports and fill up domestic stocks ahead of winter.

Ethane’s Mont Belvieu price dipped by 1.1% last week but at 37.43 cents/gal it was still the second-highest of the year. The margin contracted but remained above 18 cents/gal. The price is 51% higher than at this time in 2017 and the margin is wider by 230%.

Normal butane’s price increased by 6.4% last week to remain above $1/gal for the ninth straight week. The margin expanded by 9.5% to 82.2 cents/gal. Isobutane’s price rose 6.8% to stay above $1/gal for the 18th straight week. Its margin was 37% higher than last year’s at this time.

In the week ended Aug. 24, storage of natural gas in the Lower 48 experienced an increase of 70 billion cubic feet (Bcf), the EIA reported. The figure, compared the Bloomberg survey’s consensus average of 60 Bcf, resulted in a total of 2.505 trillion cubic feet (Tcf). That is 20.5% below the 3.151 Tcf figure at the same time in 2017 and 19% below the five-year average of 3.093 Tcf.

Joseph Markman can be reached at jmarkman@hartenergy.com or @JHMarkman.

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