{"id":4876,"date":"2026-08-27T18:01:10","date_gmt":"2026-08-27T18:01:10","guid":{"rendered":"https:\/\/discussions.weather.arizona.edu\/?p=4876"},"modified":"2026-08-27T18:01:10","modified_gmt":"2026-08-27T18:01:10","slug":"august-27th-2026-thunderstorms-will-be-more-active-in-tucson-today-with-the-potential-for-strong-gusty-winds-and-heavy-rain-phoenix-will-remain-dry-storm-chances-and-intensities-wil","status":"publish","type":"post","link":"https:\/\/discussions.weather.arizona.edu\/?p=4876","title":{"rendered":"August 27th, 2026: Thunderstorms will be more active in Tucson today with the potential for\u00a0strong gusty winds and heavy rain;\u00a0Phoenix will remain dry.\u00a0Storm chances and intensities will\u00a0increase over the weekend."},"content":{"rendered":"\n

Summary<\/h2>\n\n\n\n

Moisture from the tropics and the remnants of Tropical Storm Iselle are increasing humidity across southern and southwest Arizona. Surface observations show a surge of moisture moving up the Gulf of California, increasing the chance of thunderstorms in the region today. Forecasts predict thunderstorms developing in southeast Arizona and on the Mogollon Rim. Storms that initiate in SE Arizona will spread northwest into Pinal and Maricopa counties, with the most significant rainfall expected over the mountain areas of central Pima. <\/p>\n\n\n\n

Over the next few days, conditions remain favorable for afternoon and evening storms, particularly in Pinal, eastern Maricopa, and Tucson, with gusty winds and heavy rain likely. Activity is expected to remain high through the weekend before gradually decreasing next week.<\/p>\n\n\n\n

Yesterday’s Weather<\/h2>\n\n\n\n

Yesterday’s\u00a0visible satellite\u00a0imagery\u00a0combined with radar data\u00a0shows the extent of thunderstorm activity, with most storms near the mountains producing much more cirrus cloud cover than surface rain in Arizona. In New Mexico, the storms were strongest in the northeast and eastern portion of the state. Many of the clouds in Arizona are from former Tropical Storm Iselle. As Iselle moved north,\u00a0westerly winds\u00a0stripped the storm of mid- and high-level moisture. Over the next few days, the moisture will move across the region.\u00a0<\/p>\n\n\n

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GOES-19 visible satellite imagery and radar reflectivity from August 26th at 4 pm, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

The HRRR-UA WRF 12Z 24-hour accumulated precipitation forecast (left) and corresponding observed precipitation from MRMS (right) are shown\u00a0below. There were a few more storms observed in eastern Pinal County than forecast, and too many were forecast in south-central Pima County. Otherwise, the forecast was in good agreement with observed precipitation.\u00a0<\/p>\n\n\n

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HRRR-UA WRF 12Z 24-hour accumulated precipitation forecast (left) and corresponding observed precipitation from MRMS (right) for August 26th.<\/figcaption><\/figure>\n<\/div>\n\n\n

The isolated thunderstorms hit a few rain gauges in eastern Pima County. Santa Cruz County had a few more storms, with one rain gauge receiving 0.16 inches.\u00a0<\/p>\n\n\n

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24-hour precipitation totals from Pima County Regional Flood Control District gauges, Alert Map<\/a>.<\/figcaption><\/figure>\n<\/div>\n\n\n

Analysis<\/h2>\n\n\n\n

The National Hurricane Center (NHC) tropical weather outlook is below. The tropics are a source of late-monsoon moisture, and any tropical systems that get close to the southern tip of Baja would push moisture into Arizona. No tropical systems are in position yet.\u00a0<\/p>\n\n\n

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National Hurricane Center outlook<\/a> for the Pacific basin<\/figcaption><\/figure>\n<\/div>\n\n\n

The upper-level water vapor image below shows the jet stream moving\u00a0from northern California to northern Idaho. The source of moisture for the southwest part of the United States is the flow related to Iselle, pushing mid- and high-level moisture into the region, and moisture moving up the Gulf of California. This could be a Gulf Surge in the making or a synoptic push of low-level moisture. The Guaymas sounding\u00a0further below shows the increase in low-level moisture yesterday morning.\u00a0Either way, it should increase low-level moisture across portions of Arizona over the next few days.\u00a0<\/p>\n\n\n

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GOES-19 upper-level water vapor image August 27th at 8 am, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

Below is the observed sounding for Guaymas\u00a0yesterday morning, showing the push of moisture up the Gulf of California. The moisture has now pushed into southwest Arizona today.\u00a0The tremendous amount of Convective Available Potential Energy (CAPE) yesterday could not overcome the Convective Inhibition (CIN) since the surface didn’t reach the convective temperature.<\/p>\n\n\n

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Empalme, MX observed sounding at Phoenix for 5 am yesterday morning.<\/figcaption><\/figure>\n<\/div>\n\n\n

The Velocity Azimuth Display wind profile from Yuma shows the Gulf Surge, or synoptic push of moisture, with a depth of 3,000 feet (1 km).<\/p>\n\n\n

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Velocity Azimuth Display wind profile from Yuma radar KYUM from 7:51 am to 8:36 am.<\/figcaption><\/figure>\n<\/div>\n\n\n

The 8:00 am visible satellite picture shows a mixture of clouds with high cirrus in the northern two-thirds of Arizona and mid-level clouds in the southwest.<\/p>\n\n\n

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GOES-19 visible satellite imagery from August 27th at 8 am, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

Surface dewpoint temperatures show increased moisture across southern and southwest Arizona, driven by the Gulf Surge\/synoptic push of moisture into the state.\u00a0The increased moisture will provide more fuel for thunderstorms. Moisture has also increased in eastern New Mexico in the wake of the\u00a0cold front that swept south down the front range of the Rocky Mountains. Northern Arizona and New Mexico are still dry, but the moisture in Arizona should spread into these areas over the next few days.<\/p>\n\n\n

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Surface weather station observations for Arizona and New Mexico at 7:00 am, NWS<\/a><\/figcaption><\/figure>\n<\/div>\n\n\n

The HRRR-UA WRF 12Z initialization (left) and observed (right) sounding for Phoenix at 5 am are shown below. The moisture above 400 mb, and possibly near 490 mb, is from the\u00a0remnants of Iselle. The moisture from southwest Arizona has not reached Phoenix at the time of the balloon launch.\u00a0There is unlikely to be enough precipitable water for significant thunderstorm development,\u00a0although afternoon temperatures may cool a few degrees from the increased clouds.<\/p>\n\n\n

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HRRR-UA WRF 12Z (left) initialization and observed sounding (right) at Phoenix for 5 am this morning.<\/figcaption><\/figure>\n<\/div>\n\n\n

At\u00a0250mb,\u00a0the polar jet is in\u00a0the\u00a0Pacific Northwest, and a trough is on the east side of the ridge dropping\u00a0into Kansas\u00a0(red dashed). The subtropical ridge is centered near the western tip of the Baja Peninsula. The\u00a0Tropical Upper Tropospheric Trough (TUTT) low is further south and west than\u00a0is indicated,\u00a0but\u00a0in about the same position as yesterday.<\/p>\n\n\n

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At 500mb,\u00a0the\u00a0subtropical ridge is centered\u00a0over west-central New Mexico and is\u00a0associated with a\u00a0broad anticyclonic\u00a0(clockwise) flow, and the trough dropping into Kansas\u00a0is also visible (red dashed).\u00a0<\/p>\n\n\n

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The monsoon ridge is near the Four Corners\u00a0at 700 mb, with a broad easterly flow over northern Arizona. A couple of easterly waves are indicated from southwest Cochise\u00a0County south into Mexico and another in Big Bend, Texas.<\/p>\n\n\n

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Today<\/h2>\n\n\n\n

The forecast\u00a0sounding for\u00a0Tucson at 2 pm this afternoon (left)\u00a0shows enough\u00a0CAPE to produce storms after overcoming the\u00a0small amount of CIN.\u00a0\u00a0To the west, the\u00a0Gila Bend\u00a0sounding (right) will be right on the edge of the surge of moisture, and it’s questionable whether it can use the surge moisture\u00a0today. Thunderstorms may move into the area, jumping from mountain range to mountain range on outflows.<\/p>\n\n\n

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HRRR-UA WRF 12Z forecast soundings for Tucson at 2 pm (left) and Gila Bend at 6 pm (right).<\/figcaption><\/figure>\n<\/div>\n\n\n

Thunderstorms form around 2 pm in southeast Arizona, but don’t move into the Tucson area until 4\u00a0to\u00a05 pm. Other thunderstorms will develop across southeast Arizona east into southern New Mexico.\u00a0\u00a0<\/p>\n\n\n\n