Remember - Summer is coming from Singapore, so she is not unfamiliar with the heat Death Valley will be hotter than Singapore, but the humidity is much much lower, so that will even things out a bit - the heat will be different, but not as big of an adjustment as it is for some.

Summer - Make sure you drink a lot of water and sport water when you are in Death Valley - due to the low humidity, sweat evaporates quickly so you might not realize how much fluids you are losing. Also, with the low humidity, the sun's radiation will be stronger than you are used to, so make sure you wear sunblock and/or cover your skin - you will burn faster than you think.

I've been to Singapore. It's almost on the Equator so the sun is very intense all year.

However, Singapore is surrounded by water and the breezes make it bearable. In Death Valley, the wind can intensify the heat making it seem like you're inside a convection oven. When it's hot, there is no relief except being somewhere air-conditioned. October is usually not too bad but it can have its heat waves just as we can here in the Bay Area. October is the last gasp of summer.

I've been to Singapore too, and I am aware that it is very close to the equator

While the sun is intense in Singapore, the humidity blocks some of the sun's radiation, making it less intense than it would be otherwise. In Death Valley, while the radiation isn't as strong as Singapore due to its latitude, the sun's radiation is not attenuated by humidity. Hence my comments about the heat not being as big of an ajustment as it would be for some and the need for additional sun protection.

Not to belabor the point, but the intensity of the sun's rays in the desert of North America in October is nothing like that of the Equator at the same time of year. Use common sense, but no need to go overboard with high spfs unless one is overly sensitive to the sun.