ITHACA, N.Y. — Start stocking up on fluids and adjusting your outdoor plans accordingly; hot and humid conditions are expected from Tuesday on, with dangerous, excessive heat Thursday through Saturday.

Graphic courtesy of the National Weather Service

Excessive, Dangerous Heat Likely Late Week

At the moment, things are fairly pleasant thanks to a cold front that swept through the area Saturday night. Temperatures are seasonable and the air is fairly dry, and this pattern will last through the day Monday.

The issue will be once a warm front sweeps through the area Tuesday. This will usher in much warmer and much more humid air from the southeast. A heat dome over the southeast, and tropical dewpoints resulting from moisture brought in from the Gulf of Mexico and the remnants of Hurricane Barry, will create oppressively hot conditions and will likely result in heat advisories and potentially excessive heat warnings to be issued, especially for the time period of Thursday through Saturday.

Let’s make this clear now. Temperatures will top out in the low to mid 90s, but because of a very high humidity (the dewpoint will reach into the low and mid 70s F), it will feel much hotter to the human body – during the day Thursday, Friday and Saturday, the heat index will exceed 95 in most of Tompkins County, and in the city of Ithaca, it may reach into the low to mid 100s.

During this time period, it will be dangerous to be in the direct sun doing strenuous activity, with heat exhaustion or heat stroke possible. Please use caution if outdoors at all during the day. That means staying hydrated, taking frequent breaks in the shade, and avoiding strenuous activity if possible. If you’re a morning jogger, do it early. Wear lightweight and loose fitting clothing, and if possible, stay in an air-conditioned space and stay out of the sun.

The elderly, the ill, and those without air conditioning will be most at risk – keep an eye on your family members, friends and neighbors, and do courtesy checks to ensure their safety. Also, a car sitting in the open sun will heat up to dangerously high temperatures – do not leave children or pets unattended – “look before you lock”. We will be reporting and updating as advisories are issued and designated cooling areas are posted.

Your Weekly Weather

We’ll start off things on a quiet note with high pressure overhead. Tonight will be dry and comfortable, with only a few passing clouds and lows in the mid 50s. High pressure will remain in control for Monday, with dry air in place and a mostly sunny, low humidity day expected, with seasonably warm highs in the low 80s. Monday night, as the high shifts east and more mild and moist air starts to come in from the south, it will be a touch warmer and more humid, with lows around 60 °F and increasingly clouds.

The frontal boundary that comes in Tuesday will consist of two components – a weak frontal boundary from the west, ahead of a storm system, and an injection of tropical moisture from the remnants of Barry, which will be over the Ohio River valley. Rain is not expected to be widespread, but with the strengthening southeast flow, the humidity will be on the rise through Tuesday morning and afternoon, and it will be very muggy during the afternoon hours. Temperatures will top out around 90 °F and a heat index in the mid 90s. Some lingering showers or thunderstorms will be possible Tuesday evening, but it will be dry in most areas. It will be a sticky, humid night, with lows in the low 70s.

The low pressure storm center should sweep through Wednesday, and with it, it will be a warm, very humid day with numerous showers and thunderstorms likely, especially with daytime heating adding more energy into the atmosphere. The deep moisture layer streaming in from the remnants of Barry and the Gulf of Mexico will allow for some heavy downpours, so keep an eye out for flash flood advisories. The saving grace Wednesday is that it will be mostly cloudy, so temperatures will only rise into the mid 80s. However, with dewpoints in the low to mid 70s, the heat index will still be in the low to mid 90s. Wednesday night will be muggy and wet, with occasional rain, potentially heavy at times, and lows in the low 70s.

Thursday is when the blowtorch really starts. We’ll be under a deep layer of hot, moist air from the southwest. It will be mostly cloudy with some scattered showers and thunderstorms, with downpours possible. But the key thing to note is that temperatures will be around 90 °F with an absolutely oppressive dewpoint in the 75-76 °F range, numbers we typically only see once or twice a year, if that. The heat index will be in the upper 90s to around 100 °F. Please be careful if outdoors between 1 PM and 7 PM, it might not look sweltering at a glance but it will certainly feel that way. Thursday night should be dry but still very muggy, with partly cloudy skies and lows in the low 70s.

Friday will be the worst day, if forecast models are correct. You have a large, strong heat dome of high pressure centered over Georgia and the Carolinas, and its clockwise flow sill bring very warm, very moist air in from the Gulf of Mexico like a conveyor belt. It will be mostly cloudy with a few pop-up showers and thunderstorms around, with temperatures in the mid 90s and a dewpoint in the mid 70s. That’s a heat index of 105 °F. With that stifling, dangerous heat in place, avoid being in the sun for extended periods if at all possible, and if you have to be outdoors working, take frequent breaks to cool down. Friday night will be mostly cloudy with some scattered showers and storms, balmy with lows in the low 70s.

Saturday will be a bit less extreme but still very hot as the flow shifts slightly more westerly (and slightly drier). It will be mostly sunny, and temperatures will be in the low 90s, but with dewpoints a slightly less muggy upper 60s to around 70 °F, the heat index will be in the mid to upper 90s. Saturday night will be partly cloudy with a low in the upper 60s. Sunday will be a bit cooler but with a renewed chance of thunderstorms, with highs in the upper 80s.

Graphic courtesy of the NOAA Climate Prediction Center.

Extended Outlook

It’s looking like the heat and humidity will stick around through early next week, with a potential shift to much cooler and drier conditions for the last week of July. The heat dome will recede and allow for cooler air to penetrate from the higher latitudes, and it will come in with high pressure and persistently dry, stable air that will be much more pleasant than the week ahead.

Brian Crandall

Brian Crandall reports on housing and development for the Ithaca Voice. He can be reached at bcrandall@ithacavoice.com.